BOSTON -- A grey, damp Fenway Park on Friday was just where right-hander Aaron Cook wanted to be.

The 33-year-old sinkerballer's Red Sox debut is set for Saturday at 1:10 p.m. ET against the Orioles, and Friday marked his first game with the team.

"It's really nice. This is where I wanted to be the whole time," said Cook, who's pitched all season at Triple-A Pawtucket and had an opt-out clause on Tuesday. "To actually get the call up and be here and be with the guys I was with in Spring Training and be able to make my first start here, it's unbelievable."

Cook went 3-0 with a 1.89 ERA in five starts for Pawtucket. It's not clear how the Sox will use Cook after Saturday -- a six-man rotation remains possible with 20 games in as many days for the Sox starting Friday -- but he said he's open to pitching in relief.

"I wouldn't be opposed. Pitching here and contributing in any way is what I want to do, but you know, my main focus is [Saturday]," Cook said. "I got to go out there, take the ball, and after that, we'll worry about that."

"[I] thought more about it, but haven't made any decisions," manager Bobby Valentine said of the six-man idea. "We'll just see how these games go."

Cook said his throwing shoulder is in strong shape after the team felt in Spring Training that Cook would not be a viable relief option because of the shoulder.

"[It's] way better. I don't even know if you can put the shoulder from last year and the shoulder from this year in the same category," Cook said. "They have a really good shoulder program here. The training staff has done an excellent job monitoring everything from Day 1 of Spring Training, and it's really paid off being patient.

"My consistency is what's better. I'm not throwing much harder than I was, and I have the confidence to go out there and make pitches knowing that I'm able to just throw it and not be hurt. For a pitcher going out there, when you have confidence, that can lead to success."

Cook struck out 13 and walked 11 in 33 1/3 innings with Pawtucket.

The Sox made room for Cook on the 40-man roster by transferring Carl Crawford to the 60-day disabled list. Jose Iglesias was optioned to Triple-A Pawtucket to make room on the 25-man roster.

Beckett expects to miss only one start

BOSTON -- Josh Beckett threw from 90 feet on Friday at Fenway Park and plans to throw again Saturday, the day his start will be skipped because of a sore lat muscle.

Beckett said he was feeling better while revealing that the injury was there prior to his career-high 126-pitch outing on April 29.

"I felt a lot better today than I did the day before my last start," Beckett said. "We'll have to see how things progress. If I come in and feel [bad] tomorrow, I'll probably back off a little bit."

"He said he felt normal today," manager Bobby Valentine said. "[He] said his lat felt normal today, and then he said, 'Whatever normal is for me, but I felt normal' and he's right on schedule."

If Beckett misses just the one start, then the Red Sox would seem to have effectively gotten ahead of the matter. But that doesn't mean the Sox wish they hadn't known sooner. Beckett said he had been bothered for a week and blamed himself for not speaking up, while Valentine indicated it was pitching coach Bob McClure and the training staff whose job it was to say something.

"It's kind of been there for about a week, kind of leading into my last start," Beckett said. "You can always, on your start day, make yourself believe that things are better than they are. I really wanted to pitch. I wound up making things worse. ... I probably should have been a little smarter before my start and maybe brought something up."

Valentine called the communication matter "a snag."

"In retrospect, it would've been nice to know that," Valentine said of the injury. "We have a system set up to have information flow, it just seemed like there was a little snag there. I don't think it's up to [Beckett] to come into the manager's office. You know, you talk to pitching coaches all the time and trainers all the time. That information usually flows up."

Once the injury became known, the Red Sox did not give Beckett a say as to whether he starts Saturday, when Aaron Cook will make his season debut instead.

"They didn't really give me a choice," Beckett said. "Bobby came into the training room and said, 'You're going to miss a start.' It wasn't totally shocking when he came in and said it. It was definitely something that was discussed before that. It felt a lot better the other day. I'm pretty optimistic this next start is going to be fine."

Dice-K's rehab start rescheduled for Monday

BOSTON -- Rain's not the only reason Daisuke Matsuzaka's scheduled rehab start for Triple-A Pawtucket on Friday was pushed back to Monday.

Returning from Tommy John surgery, Matsuzaka's been bothered by the left side of his neck, particularly out of the stretch.

"Daisuke came up here and he had a little neck issue that we wanted to make sure felt perfect before he threw a 'pen again," manager Bobby Valentine said Friday. "So we kept pushing the 'pen back. I should've told you all. He wasn't really scheduled to pitch today, even though we wanted a lot of the press to go there, help out the economy in Toledo [where Pawtucket would've been].

"We talked on, I guess, Tuesday and Wednesday, and we said we'll revolve his next start around his bullpen availability, his neck condition. Today is going to be his bullpen day -- or tomorrow, depending on how he felt when he played catch -- and he can pitch Monday. I think we'll have better weather. Initially, the [thought of a pushback from Friday] was the weather concern, and then it became a neck concern.

"It's his left side. Out of the stretch mainly. It had nothing to do with his throwing -- [he] felt great throwing. Rather than having him pitch with any kind of ailment, we got it better. He feels great."

Instead of pitching on the road, Matsuzaka's first start for Pawtucket is scheduled at home, against the Twins' Triple-A club, Rochester, in a 6:15 p.m. ET start.

Pitchers can rehab in the Minor Leagues for a maximum of 30 days. Matsuzaka's first rehab game was April 23, and Valentine projected Matsuzaka would have two Minor League starts (including Monday's) or maybe three, if Monday's outing is brief -- but that would seem to be too few if Matsuzaka is to pitch on an every-five-days schedule.

"As many [outings] as he thinks he needs," Valentine said. "But there is a rehab assignment date which becomes a technicality, which should give him at least two more starts."

Red Sox convey concern, respect for Rivera

BOSTON -- The Red Sox had concern for Yankees closer Mariano Rivera on Friday, even though their own on-field success might be bolstered by the absence of the universally respected future Hall of Famer.

Rivera tore the ACL in his right knee while shagging fly balls during batting practice on Thursday and is out for the season.

"Mariano, man, I always say he's the best pitcher in the game I've ever seen," David Ortiz said. "Period. Simple. One pitch."

"What do you say? I mean, he's the greatest closer ever," Hall of Fame closer Dennis Eckersley said. "That's not the way he wanted it to end. And I don't know if it is the end."

Told Rivera had announced Friday afternoon that he would indeed make a return attempt, Eckersley was glad to hear it.

"Makes sense. Makes sense," Eckersley said. "If you think about it, he can. And it gives him some incentive. He didn't want to go out like this. He won't shag anymore. I've seen a lot of guys and I've seen guys get hurt. But that's what he does. But you know, and you see the replay, it was nothing, probably compared to some of the ways.

"If it was over, it's easy for me to say, 'He never had a bad year. So he gets to walk away sort of like that. But now he can come back.'"

Ortiz and manager Bobby Valentine spoke of their reverence for Rivera before the news broke that Rivera would try to come back.

"It was sad, man," Ortiz said. "Mariano is a guy that ... good people, man. Good people. Last night when I saw it on TV, it was pretty emotional. Going out the way he did was unbelievable. He was doing what he was supposed to do. Injuring himself like that, I guess you don't expect it, but it happens. We come in early, we do our workout. If you get injured working out, doing what you're supposed to do, there's nothing you can do about it. It was pretty sad, seeing him last night going through what he went through. You don't want to see anyone getting injured, especially a guy like Mariano.

"Me and Mariano, we are really good friends. He's the kind of person that's a major believer in, God has something always planned for us. I'm pretty sure if that's the way God wants him to finish his career, he'd understand that, he'd agree with it."

Valentine, as manager of the Mets, saw up close as a younger Rivera closed out the 2000 World Series.

"I liked my closer [Armando Benitez] at the time, too, and the series kind of went because one of their batters had a great at-bat against our closer and we didn't have any great at-bats against Mariano," Valentine said. "But 2000 he was great. And we knew that. The plan was to not get him in the game, not beat him once he got in. We didn't follow the plan. Or we didn't execute the plan.

"Mariano, everybody knows, I can only be redundant in anything that I say because he's one of the greatest guys I ever met. Obviously one of the great athletes who was doing an athletic event when he got hurt. Goes without saying, the kind of pitcher he was, I don't think I'll ever see it in my lifetime again. He's special, hopefully he can come back, even though he's with the bad guys."

Valentine said the Yankees would feel Rivera's loss if their starters can't go deep into games.

"I think it'll depend on their starting pitching. If they're going to the sixth and seventh a lot, I think they're going to miss him," Valentine said. "If their starting pitching stretches out into the eighth inning, they might be OK. [It's] still not going to be as comfortable a feeling, for sure."

Red Sox may be in a pinch with 13 pitchers

BOSTON -- Aaron Cook's addition means the Red Sox are back to a 13-man pitching staff and a small, three-man bench. That will limit how much manager Bobby Valentine can play late-game matchups with opposing pitchers.

"We have a pretty short bench, and pinch-hitting isn't one of the real options that we're going to be dealing with here in the near future," Valentine said.

Valentine said he won't hesitate to use the day's backup catcher -- Jarrod Saltalamacchia starts against righties and Kelly Shoppach against lefties -- as a pinch-hitter, even though it leaves open the possibility of needing an emergency catcher.

"I don't mind. As long as they can hit, yeah, I don't mind," Valentine said. "Tonight'll probably be the night, but the only time I caught was because three catchers got hurt. And I had one position player have to catch in 3,000 games that I've managed. We could get by if something crazy happened. One day."

Asked if Nick Punto would be the go-to backstop if Shoppach and Saltalamacchia were out, Valentine said it depended who was available.

Valentine also played with the lineup by debuting Will Middlebrooks in the No. 2 spot Friday against the Orioles, in the third baseman's second big league game. Middlebrooks went 2-for-3 with a double, walk and strikeout in his debut Wednesday in a 4-2 loss to the A's.

"I asked if he ever hit second before, he said 'No,'" Valentine said. "[I] asked him, 'What are you going to do different?' He said, 'Nothing,' which is the right answer. I asked him, 'What do you think,' he says 'Let's go for it,' so he'll get his at-bats and we'll see how that looks here in this grouping. ... I liked his at-bats the other day, and to give him another at-bat might be a good thing. We'll see."