SAN FRANCISCO — As the Orioles opened their three-game interleague series against the San Francisco Giants on Friday night at AT&T Park, setup man Darren O'Day was traveling back to Baltimore to get his right shoulder examined today.

Orioles manager Buck Showalter said O'Day felt some “posterior shoulder discomfort” during his outing Thursday in Oakland, where the right-hander allowed two runs in one-third of an inning and let an inherited runner score.

O'Day will miss the series in San Francisco, and maybe more time depending on team orthopedist Dr. Michael Jacobs'evaluation.

“I feel pretty confident he would not have pitched here with what he told us yesterday,” Showalter said. “We have some hope that something could resolve itself by Tuesday or Wednesday.”

The Orioles will recall Triple-A Norfolk right-hander Tyler Wilson if it becomes clear O'Day will need to go on the disabled list. Wilson is on the taxi squad and must officially be added to the 25-man roster by today or be returned to the minors.

“We're hoping it's something that will resolve itself quickly,” Showalter said. “It's yet to be seen whether they'll inject O'Day [with cortisone] or not. I don't know if they'll do it tomorrow. With the off day [Monday], we probably wouldn't have pitched him today or the weekend. It was prudent to get him there. If we get some type of news from Dr. Jacobs, we don't want to [have to] get a guy across the country, so we thought it was smart to get Tyler out here.”

Showalter said Thursday was the first time O'Day complained about a shoulder problem. But O'Day has yielded five earned runs over his past three outings spanning 12/3 innings. In those outings, O'Day let seven of the 12 batters he faced reach base.

“He said that yesterday was the first time” he felt pain, Showalter said. “He had some real good outings since he's been back. I know you don't forget that, and he's had a couple where it wasn't. Now I don't know how forthcoming [he has been]. I know Darren wanted nothing to do with going back on the DL, but he's also not going to do anything to hurt the club. He actually wanted to stay and pitch through it, but we just didn't think that was a very good idea.”

O'Day, who signed a four-year, $31 million deal in the offseason to remain with the Orioles, missed nearly eight weeks with a strained right hamstring. He pitched five straight scoreless outings after his return July 24 before being scored upon in two of his past three outings.

Orioles recall Hart for lefty relief: The Orioles recalled left-handed reliever Donnie Hart from Double-A Bowie before Friday night's game as the club continues to search for situational bullpen help against left-handed hitters.

Hart had a nine-day stint with the major league club last month, pitching 22/3 scoreless innings before he was sent back to Bowie when O'Day returned from the disabled list.

Hart pitched almost exclusively to left-handers while with the Orioles, holding them to one hit in six at-bats with one walk and a strikeout. At Bowie, he has held left-handers to a .188 batting average.

Though his first stint with the Orioles was brief, Hart said he returns to the majors having learned a lot.

“I think the biggest thing is that these hitters are going to hit mistakes, but if you make your pitches you're going to get outs,” Hart said. “Even when you do make your pitches, you might get hit, but [getting] strike one, that's the biggest thing on my mind. I've got to get ahead of guys here and if I can do that I think I'll give myself a chance to have some success up here.”

The Orioles needed to improve heading into this weekend's series — the Giants can stack eight left-handed hitters in their lineup — and they optioned right-hander Logan Ondrusek to Bowie after he continued to struggle getting lefties out.

Ondrusek, who was signed after pitching in the Japanese Central League for his ability to get lefties out, allowed six of the 10 left-handers he faced to reach base. Lefties were 4-for-8 with three extra-base hits (two doubles and a homer) and two walks against Ondrusek.

Wilson on taxi squad: Wilson made a cross-country flight from Norfolk to join the club in San Francisco in case he's needed in O'Day's absence. Officially, he was on the 24-hour taxi squad, meaning the Orioles must recall him over the next day or return him to the minor leagues.

Wilson has been up and down between the majors and Norfolk often this season, and he's one of the first pitchers the Orioles have called upon when they've needed an extra arm, whether for a spot start or relief.

“It's happened quite a bit now,” Wilson said. “That phone call never gets old. It's always great to be here and be a part of the great things this team is doing right now. Whatever happens the next day or 24 hours or whatever, it's just the beginning. We're at a good place as a team, and I'm just happy to be here to be a part of it.”

Pearce making strides: Infielder-outfielder Steve Pearce took one step toward avoiding the DL by taking batting practice before Friday's game, the first time he has hit since leaving Sunday's game with a right flexor mass strain.

Showalter, who said Pearce was an option to pinch-hit Friday, said he'd like to get Pearce into the lineup for tonight's game against left-hander Madison Bumgarner.

“It will be a little tougher with the National League rules,” Showalter said.

Around the horn: Outfielder Joey Rickard, who is on the DL with a right thumb ligament injury, will see hand specialist Dr. Kenneth Means on Wednesday. “They pushed it up a day, so we'll see,” Showalter said. “It will be good to hear what he has to say.” … Left-hander Brian Duensing (left elbow inflammation) threw a 25-pitch bullpen session Friday. … Bowie left-hander Chris Lee (lat muscle soreness) is throwing from 60 feet on flat ground.

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