Manager Joe Girardi said Gardner had a bruised right elbow and a muscle strain in that area, as a result of a diving catch he made in the third inning of New York's 8-3 win on Tuesday.
"He took [batting practice] today and said he felt fine, but when he went to take his swings today in the cage at 6:20 or 6:30, he wasn't fine," Girardi said after the Yankees' 6-5 loss Wednesday. "So at some point in between that time, it must have really flared up. So we sent him to get an MRI, and that's what the diagnosis was."
Gardner said after the game Tuesday that he experienced some wrist soreness after the play, but it had subsided by game's end and he did not expect it to be a lingering issue. But he was scratched from the starting lineup shortly before the first pitch Wednesday.
The outfielder was 2-for-2 with two doubles, two walks and a stolen base Tuesday.
Girardi said he's likely to turn to Raul Ibanez and Andruw Jones, who played left field on Wednesday night, to fill the void. Eduardo Nunez could get a look there, as well.
"I take my ground balls, my fly balls every day, I throw to bases every day, so nothing really changes," said Ibanez, who was 2-for-4 on Wednesday, playing right field. "You prepare to play baseball, to be a baseball player and help your team win. It's very unfortunate -- Gardy's a huge part of our club, and it's very unfortunate."
If there's a silver lining, it's that the club will take the opportunity to get some much-needed bullpen help in Gardner's place. Girardi said the Yankees will call up right-hander Cody Eppley, who was claimed off waivers from the Rangers on April 5.
Eppley appeared in 10 games for Texas last season, allowing eight earned runs in nine innings of work. He has thrown 6 1/3 innings of scoreless ball for Triple-A Scranton/Wilkes-Barre this season.
The Yankees' bullpen has been taxed early on this season because of the starting pitching struggles. The rotation has just three quality starts this year.
"It's too early," catcher Russell Martin said. "We're not going to be in panic mode. I trust our pitching staff to get it going. Just some little bumps along the way right now."
Jones played left field Wednesday night and went 0-3 at the plate with two strikeouts, while struggling at times to find his bearings in the outfield.
Gardner has three multihit games this season, and was 3-for-11 with five runs, two doubles, an RBI, four walks and one stolen base on the homestand.