O'Day won't fly with the team to Toronto later tonight, according to manager Buck Showalter, and may visit hand specialist Dr. Brian A Schofield in Sarasota.
Showalter hadn't confirmed O'Day's condition until this afternoon while meeting with reporters. He touched on the subject about halfway through his 30-minute session.
"Darren O'Day's not going with us on this trip," Showalter said. "That's the plan. He had some tests today. They've done a great job, our doctors and the people here in Baltimore, getting all the tests done, trying to figure out how long and what we're dealing with here.
"There's some pain there. We're just trying to get ahead of it, to be frank with you, because you won't see him in Toronto. We're just trying to get our hands around what's causing it, because they've done a lot of structural tests, they've done a lot of blood and nerve. Just trying to get an idea of exactly what's causing it.
"His fingers are sore at certain times. It's kind of gone back and forth. He had a couple days where it didn't bother him at all, and then it came back again.
O'Day has pitched only twice since Aug. 28, most recently going two innings on Saturday. He's 5-3 with a 2.28 ERA in 63 appearances, with 46 hits, 14 walks and 57 strikeouts in 59 1/3 innings.
The issue with his fingers cropped up "one to two weeks ago," Showalter said, "but it's been very small and there were days when he didn't have any problems at all. And then it's kind of gotten more frequent and closer and we don't like it.
"It came up just trying to test it a little bit in the outfield before a game during BP."
Showalter didn't completely rule out the possibility that O'Day could rejoin the team in Toronto. Or it could happen later in the road trip, which includes stops in Boston and Tampa Bay.
"It would be hard with the symptoms he's presenting, in doctor's speak, that he would be available to us in Toronto, but it could happen," Showalter said.
Doctors are testing O'Days hand and elbow.
"I'll tell you what, he's had the gamut," Showalter said. "You name one. There's vascular, there's structural, there's nerve. There's really three things. Just trying to identify which one is creating the issue.
"I've become an expert on it. Believe me. I get drilled on it every day."
O'Day was 7-1 with a 2.28 ERA in 69 games last season. He signed a two-year extension over the winter that includes a club option.
O'Day gets $2.2 million this season and $3.2 million next year. The option in 2015 is worth $4.25 million and includes a $400,000 buyout.
The Orioles rely heavily on O'Day, who pitched with minimal rest down the stretch and in the playoffs last season. Showalter has been forced to alter his usage of the bullpen this month.
"I present it as something that opens up an opportunity for somebody else to present themselves well," Showalter said. "We found some orchids(last year) while searching for roses, and having a rose missing, and Darren's been that.
"It's killing him because he sees situations and I'm sure you guys at times upstairs may assume something that happened with the bullpen. You've seen me enough to have an idea that may have been a little break. That had a lot to do with it. Especially this time of year with the 40-man rosters, they can go left, right, left, right, left, right the whole way. It's a different game. That's why we believe what's going on with 40-man rosters is crazy. It's a different game. It creates some different things.
"I challenge our guys to, if somebody falls, somebody's got to take his place in the artillery line or whatever."
Here's the Yankees lineup:
Brett Gardner CF
Alex Rodriguez DH
Alfonso Soriano LF
Robinson Cano 2B
Vernon Wells RF
Eduardo Nunez 3B
Mark Reynolds 1B
Brendan Ryan SS
Chris Stewart C
Phil Hughes RHP