ST. PETERSBURG -- The Rays placed outfielder Gabe Kapler on the 15-day disabled list Monday with a mild right ankle sprain, clearing up a roster spot for first baseman Carlos Pena to return.

Kapler said he sustained the injury during a collision at the plate Saturday with Orioles catcher Matt Wieters. Kapler was forced to run home on the play and hoped to bowl over Wieters after a baserunning gaffe by B.J. Upton that resulted in both players standing at third.

"I just pushed off with my right foot and felt a little twist there," Kapler said. "It is what it is -- a mild ankle sprain."

Kapler said he hasn't dealt with anything like this before, but he and the trainers thought it would be best to take care of it sooner rather than later. The stint on the disabled list is retroactive to Sunday, so Kapler will likely return around Sept. 1, when Major League rosters expand to 40 players. Kapler couldn't guarantee he would be back by then, instead stressing the importance of a full recovery.

"As we've seen in the past, the sooner you can jump on minor injuries, the sooner they jump back for you and you can perform at your highest level," Kapler said. "I'm not here to make any predictions. I know that we needed to jump on it and knock it out, and I'll be healthy in due time."

Manager Joe Maddon said he hoped to have the right-handed-hitting outfielder back by Sept. 1. In that case, no one would have to be sent down or released to make room for Kapler's return.

"It kind of worked out that we were able to DL him today as Carlos came back," Maddon said. "Kap will be ready probably by the first of September."

Rays activate Pena from disabled list

ST. PETERSBURG -- Carlos Pena returned from the 15-day disabled list on schedule Monday, batting cleanup and playing first base for the Rays.

Pena, out since Aug. 1 with a right plantar fascia sprain, said it felt good to be back with the team, and although he thought he might feel "some discomfort," he said he doesn't expect the foot injury to be a problem going forward.

"I feel good. We're just going to keep progressing, taking care of it, being smart with all the treatment and all the necessary exercises to maintain myself," Pena said. "That's it. I think I should just keep on progressing and shouldn't have any type of difficulty doing that. I don't expect anything to go wrong. On the other hand, I expect everything to go very smoothly.

"I've been really working hard and putting a lot of stress on it over the last week and a half, and it's responded very well. I don't expect it to go backward on me or to get tired or anything like that. I think we've done all that we can."

Pena played a rehab game with high Class A Charlotte on Sunday night, going 2-for-3 with two singles and an RBI as the team's designated hitter -- an encouraging sign for manager Joe Maddon.

"Carlos had a nice day yesterday -- no repercussions, felt really good, hit the ball well," Maddon said. "And they did shift him. We wanted to check on if they did shift him in the Minor Leagues, but Los came through and he's ready to roll."

Maddon added that he would keep an eye on Pena to make sure he feels comfortable on the field, particularly on defense, but he wasn't worried about his ability to run the bases. He noted that he would likely check in with Pena later on in each game to make sure he doesn't need a replacement -- but only if it is absolutely necessary.

"I don't want Carlos off the field if he feels like he can play first base," Maddon said, "So that'll be a discussion on a daily basis with him to find out how Carlos feels."

Pena wasn't as worried about the potential pain, as he was just excited to rejoin the Rays, especially as the team enters the home stretch of what should be a tight pennant race with the Yankees and Red Sox.

"It feels so good, it really does," Pena said. "It feels great to be back. We're in a good position and want to be even better, so we've just got to keep on going."

Niemann, Davis throw bullpen sessions

ST. PETERSBURG -- Right-handers Jeff Niemann and Wade Davis continued their rehab from right shoulder strains Monday afternoon by throwing bullpen sessions, and both are on track to return to the Rays next week after going on the disabled list almost two weeks ago.

Pitching coach Jim Hickey said the bullpens went "very well." Niemann threw about 43 pitches while Davis threw 49. Both will throw another side session on Wednesday before progressing to a simulated game Friday in Oakland. After that, Davis is set to start Aug. 24 against the Angels, with Niemann getting the nod the day after.

Hickey reported that Niemann used all of his pitches well and almost at game speed, exactly as he planned to, but Davis might have looked even better Monday.

"They were close, but I think Davis had a little bit more effort and little bit more of a finish on the ball," Hickey said.

Niemann thought he was a little off, though he wasn't surprised by it given the amount of time he's spent on the disabled list, but he still felt no pain in his strained right shoulder.

"I felt great today," Niemann said. "Everything felt great. Every day's been a marked improvement since we've been here, so that's been the best thing about it."

Rays manager Joe Maddon said putting the two right-handers back in the rotation on back-to-back days could create a difficult situation for the team's bullpen, as they likely would not be able to throw as deep into the game as usual, so he would consider spreading them out. The plan for now, however, is to have them pitch on consecutive days against the Angels.

"The way we have it loaded up right now is that we're looking at them both in Anaheim," Maddon said. "I've just got to talk to them and find out. If there needs to be a little gap, and part of the gap could be created by our bullpen issues or situations at that time, they both can be ready back-to-back days. That's potential. But we haven't really got into the heavy discussions of if that's wise or not yet."