Gardner has been on the disabled list since April 18 because of a bruised right elbow and a strained arm muscle.
"It's the muscle that he strained, that healed, that he's re-strained basically," Yankees manager Joe Girardi said. "He will not pick up a bat for 10 days, and then we'll go from there."
"I don't necessarily think this is a three-month thing," Girardi added. "But, unfortunately, I think we're gonna be without him for another 15 to 25 days."
Gardner, 28, was off to a good start this season for the Yankees. He was hitting .321 with a .424 on-base percentage in nine games. Last season, in 159 games, Gardner hit .259 with seven home runs, 36 RBIs and an American League-best 49 stolen bases.
"We miss him. There's no doubt about it," Girardi said. "The way he was swinging the bat, his defense, the way he puts pressure on defenses -- we miss his presence in left field. But we have to find a way to get it done without him."
Gardner suffered the injury while making a sliding catch in a game against the Minnesota Twins.
"It's not something structural, it's a muscle, we know that will heal," Girardi said. "But it's frustrating."