WASHINGTON -- Orioles catcher Matt Wieters wasn't in Friday's starting lineup against the Nationals as manager Dave Trembley opted to be cautious with the young backstop, who was sporting a nice bruise after fouling a ball off his right knee in the third inning of Thursday's 13-7 loss to Texas.

"You have adrenaline going through the game, [and] I kept moving, so it was fine [Thursday night]," Wieters said of his knee. "But after a three-hour plane flight and getting in real early [Friday] morning, it got tight on me. So just give it a day and we'll be good to go."

Trembley said X-rays on Wieters' knee came back negative, but he would try to stay away from using him on Friday, even in a pinch-hitting situation. Wieters, who turned 24 on Friday, has appeared in 37 of the team's 43 games.

Wieters was optimistic he would be sidelined for only one game and anticipated Friday's off-day would take the place of Sunday afternoon, which was his originally scheduled day off.

"[I'll] play the next two games [of the series] and be 100 percent, instead of 60-70 percent," Wieters said.

"It's not like a pain, it's just a stiffness."

Wieters is hitting. 255 this season and is coming off a 2-for-10 road trip in Texas, where he also had a walk and an RBI. He has thrown out 11 of 26 potential basestealers this season and committed just one error behind the plate.

Uehara unavailable following taxing outing

WASHINGTON -- In order for Orioles reliever Koji Uehara to be effective and injury-free, the team has to be extra cautious with his workload and the weather conditions.

"I feel like you almost have to script it with him, to be honest with you," manager Dave Trembley said prior to Friday's game.

"We have to be guarded with [Uehara] and get him into a little bit better baseball shape."

Uehara was not available for Friday's series opener against the Nationals because Trembley and pitching coach Rick Kranitz felt it was best to give the reliever a pair of days off following a 30-pitch outing on Wednesday. Uehara recorded just two outs in the Orioles' 4-3 loss to the Rangers, but appeared to be physically drained in the Texas heat.

"He was absolutely spent," Trembley said. "He has not pitched in those kinds of conditions all year, coming in the middle of an inning, a real good lineup, men on base, it was warm for him."

On Friday afternoon, Uehara said through interpreter Jiwon Bang that the weather wasn't a factor so much as the number of pitches thrown.

"I don't look at it as the heat being an issue," Uehara said, adding that Kranitz and Trembley informed him of their decision to rest him following Wednesday's game. Uehara also said he feels he is conditioned enough to pitch in the humidity.

After spending most of the spring on the shelf -- he was placed on the 15-day disabled list with a left hamstring strain retroactive to March 26 -- Uehara returned to the Orioles on May 6. But given the ease of his rehab outings -- the longest of which was 14 pitches -- Uehara's arm strength may be a concern for the team going forward.

"I don't think he is up to where everybody else is, because he didn't pitch that much," Trembley said.

"And [the rehab] wasn't really taxing on him. It was, guys throwing in extended spring training, its not like he was throwing to [Rangers hitters] Ian Kinsler, Michael Young and Vladimir Guerrero. I would think there's a little more stress trying to get those three outs then there is trying to get kids out in extended spring training."