As one major leaguer returns from the injured list, the Orioles have lost two to the sidelines.

The Orioles’ outfield depth grew thinner when they placed Colton Cowser on the seven-day concussion injured list Friday, retroactive to Thursday. Additionally, outfielder Tyler O’Neill was placed on the 10-day injured list, retroactive to Wednesday, with right wrist inflammation.

In their places, Baltimore activated first baseman Ryan Mountcastle from the 60-day injured list and recalled outfielder Jordyn Adams. The Orioles also signed outfielder Greg Allen and are immediately placing Allen in center field against the Athletics on Friday.

Interim manager Tony Mansolino said Baltimore signed Allen because the club is in need of outfield help. However, when asked whether the Orioles considered calling up outfielder Dylan Beavers — who is raking for Triple-A Norfolk — Mansolino said he wasn’t involved in those decisions.

“I know [general manager] Mike [Elias] and the front office, they have a very specific plan in place for that,” Mansolino said. Beavers is hitting .309 with a .961 OPS for the Tides.

Mountcastle is in the lineup for Friday’s series opener against the Athletics as the designated hitter.

“I feel good,” said Mountcastle, who is returning from a hamstring strain. “Rehab went well. Thanks to all the staff and all them; they were great. Just happy to be back.”

Cowser suffered the concussion in the sixth inning of Wednesday’s win when he went to catch a fly ball by Harrison Bader and hit the left-field fence in Philadelphia with force. Cowser appeared to be in discomfort after the play. He grimaced and put his hands on his knees, but he remained in the rest of the game.

Mansolino said Cowser’s concussion symptoms developed after the finale against the Phillies.

“Very mild in nature is the hope right now,” Mansolino said. “No timeline, but I would probably hope, speculate, it won’t be any more than the minimum.”

Cowser has had a difficult season, which began with him landing on the injured list for a broken thumb March 31. Since returning in June, Cowser has yet to find his form. He’s hitting .213 with a .680 OPS.

Before his 1-for-4 performance in Wednesday’s win, Cowser had struck out 14 times in his last seven games (20 at-bats).

O’Neill injured his wrist Tuesday night in Philadelphia when he collided with the wall. He remained in the game for another at-bat, but he said the aggravation of his wrist forced him out. His X-rays Tuesday were negative, he said, but O’Neill received additional imaging Thursday.

Mansolino said O’Neill is receiving multiple opinions on his wrist inflammation and is “not quite sure what to think about it yet. Hoping, cautiously optimistic that it’s not significant.”

This has been a challenging year for O’Neill, and it’s part of a challenging career in terms of injuries. He made two previous trips to the IL this season, one for his shoulder and another for his neck.

To assist with the outfield depth, the Orioles signed Allen to a major league deal. The 32-year-old opted out of his minor league contract with the Chicago Cubs’ Triple-A affiliate Monday. Allen, a switch hitter, was batting .270 with a .795 OPS in Triple-A.

Allen takes the roster spot of utilityman Vidal Bruján, who was claimed off waivers by the Atlanta Braves on Friday.

Mansolino managed Allen in 2019 in Cleveland’s farm system. The Orioles were also familiar with Allen from his time with the New York Yankees in 2021 and 2023, when he played a combined 37 games.

“First of all, can play center field, can bunt, run, looks great still,” Mansolino said.

Mountcastle played nine games for Triple-A Norfolk before his return Friday, and he had a front-row view of Beavers and top prospect Samuel Basallo. Both players are knocking on the door for a debut.

“They’re really good,” Mountcastle said. “A lot of good players down there, and a lot of bright futures ahead of them, and excited to see them up here at some point.”

Rico Garcia returns

The Orioles activated right-hander Rico Garcia on Thursday, and he returns to an organization for which he pitched eight innings in 2022. He has bounced around since then, joining the Washington Nationals in 2023 before splitting time with the Yankees and New York Mets this year.

Garcia should bolster a thin bullpen. He recorded a 2.13 ERA in 12 2/3 innings for the Mets before he was designated for assignment and claimed by the Orioles.

Garcia said his improvement stems from the introduction of a gyro slider while pitching last year for Triple-A Rochester, part of Washington’s farm system.

“This year, kind of just incorporated that more and kind of shied away from throwing fastballs in leverage counts,” Garcia said. “I kind of got in trouble previous years in doing that and have kind of just been focused on throwing more off-speed in those hitter-advantage counts.”

Garcia tried to add a sweeper in 2022, but he didn’t master it. His new slider has 0-0 movement, he said, which means it tends to flutter in place. Rather than dropping or sweeping early, the offering fools hitters by relying on its corkscrew-like spin and late dip.

Batters have yet to record a hit against that pitch this season, according to Statcast. And they have whiffed on 41.2% of their swings against gyro sliders Garcia has thrown.

“I was trying to get that sweep before, but I think I’m the kind of pitcher who just needs to rip it and not really think about getting a certain angle on the ball,” Garcia said. “So the slider is going to be from 86 to 88 [mph], and it usually has 0-0 movement.”

This article has been updated.