BALTIMORE -- It was a welcome sight to see Orioles second baseman Brian Roberts on the field taking ground balls and playing catch prior to Tuesday's series opener against the Athletics.

"Roberts is back, he got cleared by Doctor [William] Goldiner [Tuesday]," manager Dave Trembely said. "He'll resume some baseball activities and in all likelihood when we leave [for Toronto following Thursday's game] he'll be on his way to Florida to see if we can get that going."

Roberts was originally scheduled to go to Sarasota, Fla., during the team's last road trip -- which started May 19 in Texas -- but he was hospitalized with pneumonia on the Monday prior, and has remained in Baltimore since.

When Roberts departs for Florida later this week, he will report to the team's Spring Training complex in Sarasota with the expectation being that he will gradually work his way back into baseball shape.

Roberts has been sidelined since April 9 with a herniated disc in his lower back, an injury that was originally suffered during offseason workouts but was reaggravated during a slide into second base in the team's home opener.

Scott misses opener with shoulder strain

BALTIMORE -- Orioles designated hitter Luke Scott has a left shoulder strain and was a last-minute scratch from Tuesday's series opener against the Athletics.

"Luke said diving for the ball [in the 10th inning on Sunday] on the play that Al [Simon] pulled a hamstring, he jammed his shoulder," manager Dave Trembley said. "[Scott] said it was really bothering him in batting practice [on Tuesday], so we decided not to play him."

Trembley wasn't sure if Scott would be ready to play on Wednesday given that he was told Scott "really couldn't swing" Tuesday afternoon.

Scott was originally in the lineup batting fifth. He was replaced by Garrett Atkins, who assumed the No. 8 spot and snapped an 0-for-18 streak with a seventh-inning single. Ty Wigginton moved from the second position to the fifth and extended on his team-leading 32 RBIs with a sacrifice fly in the sixth inning.

An Orioles lineup without Scott for any length of time would certainly be a blow to an already injury-plagued team. Scott has hit in 12 of his last 14 games, going 22-for-52 (.423) with three doubles, six homers and 12 RBIs over that stretch.

For Atkins, Tuesday's start was his first since the Orioles' loss to Texas on May 19. Atkins is hitting .222 on the year and is marred in a career-high homerless drought of 47 games.

Relievers Castillo, Mata added to roster

BALTIMORE -- The Orioles recalled Alberto Castillo and purchased the contract of Frank Mata prior to Tuesday's series opener against the Athletics. The pair of relievers will assume the roster spots vacated by Koji Uehara and Alfredo Simon, both of whom were placed on the 15-day disabled list.

To make room for Mata on the 40-man roster, the Orioles moved Mike Gonzalez (left shoulder strain) from the 15-day DL to the 60-day.

Castillo (1-0, 12.79 ERA) will be joining the Orioles for the third time this season, and was most recently optioned back to Norfolk following Thursday's loss to the Rangers. Given that Castillo didn't pitch well his last time out -- allowing four earned runs on four hits over just 2/3 innings in Texas -- he said he was surprised to get the call.

"But they've seen what I can do [in the past]," Castillo said.

Castillo has appeared in 48 games with the Orioles over the last two seasons, going 1-0 with a 3.32 ERA, and he will provide manager Dave Trembley with another left-handed option to go with long man Mark Hendrickson and lefty specialist Will Ohman.

The 26-year-old Mata will be making his Major League debut. A closer with Triple-A Norfolk, the right-hander recorded eight saves and was 2-1 with a 1.86 ERA in 18 games.

"Mata will be really excited to be here," Trembley said. "I know what his history is and what he's done, but I'm not at this particular point in time able to say what role he'll be in. He's in the bullpen."

Castillo and Mata will join starter David Hernandez -- who was also moved to the 'pen prior to Tuesday's game -- in giving Trembley a wealth of options. Ravaged by injuries, the O's have an eight-man bullpen and are hoping to find strength in numbers.

"It's challenging," Trembley said when asked if this was the most uncomfortable bullpen makeup in his nearly three years at the helm.

"But you never know, somebody might step up and it could not only be interesting but it could provide an opportunity for somebody to really make a name for themselves. So. that's how I look at it."