Gardner felt pain in his right elbow on Saturday morning and will be sent to see Dr. James Andrews in Pensacola, Fla., early next week. He will also be seen by specialist Dr. Timothy Kremchek in Cincinnati.
"Medicine is an inexact science," Yankees general manager Brian Cashman said. "It's a Rubik's cube that we still have to solve on him."
Gardner had three at-bats for the Riverdogs in a 5-1 victory over Savannah on Friday, playing five innings in the field. The Yankees had been optimistic that he would rejoin the team on Monday in Atlanta.
That will not happen, and manager Joe Girardi said that he now fears Gardner will not return until after the All-Star break, at the earliest.
"Obviously, it's a setback, and I don't know when we'll see him now," Girardi said. "I said if he had another [setback], my thought was it would be after the All-Star break, so there's concern we're not going to have him for awhile."
The setback is the second at the Minor League level for Gardner, who has not played in a Major League game since April 17, when he made a tumbling catch in left field and strained his elbow. He had been close to re-joining the Yankees in May before again feeling pain.
"He seems to get to a point where he can do everything he needs to do, and then when he plays in a game, maybe it's the intensity being turned up a little bit; some swinging and missing," Girardi said. "It seems to bother him."
Cashman said that he needs to be careful with how much the Yankees play veterans Raul Ibanez and Andruw Jones in the outfield, but said he has not started pursuing any outfielders on the trade market.
"Joe's doing his best to protect them, but we expected Gardy back twice already, and it hasn't worked out for us," Cashman said. "No one's more frustrated than Gardy, and we're next in line in that."