Brett Gardner left Thursday night's game against the Baltimore Orioles after feeling a twinge in his rib cage on a check-swing strikeout leading off the game.
The New York Yankees have traveled to Boston to face the Red Sox this weekend while Gardner stayed back in New York to have an MRI.
"I have no idea. I've never dealt with anything like this before," Gardner said of the severity. "But it felt serious enough for me to say something and come out of the game. So you take what you want from that. I don't think anything's broken, obviously, but it's just one of those things where I've never had an issue before, and I know something's not right."
Gardner is hitting .273/.344/.416 with eight home runs, 52 RBIs and 24 stolen bases this season.