The club said Chamberlain will rest for about a week before beginning a throwing program. Chamberlain had gone to see noted orthopedic surgeon Dr. James Andrews after undergoing an MRI on his ailing right shoulder Tuesday.
Yankees manager Joe Girardi called it "a pretty good diagnosis," but said he didn't have a best-case scenario for Chamberlain's return.
"He'll pitch when he's ready," Girardi said.
The 22-year-old right-hander was removed from Monday night's start against Texas in the fifth inning with stiffness in his shoulder.
Chamberlain was moved from the bullpen to the rotation this season. He is 4-3 with a 2.63 ERA in 32 games, including 12 starts.
His injury is the latest blow to New York's depleted pitching staff. The team is already without No. 1 starter Chien-Ming Wang and right-hander Phil Hughes.
Ian Kennedy is expected to be called up from the minors to start Friday, when the Yankees continue their 10-game road trip at the Los Angeles Angels. Dan Giese will start Saturday.
"You lose your No. 1, and you lose another guy that's been throwing the ball well for you in Chamberlain, it's things you have to deal with," Girardi said. "You've got to move on. That's the only thing you can do in this game."
Yankees shortstop Derek Jeter echoed that approach.
"You can't sit here and hang your head about it," Jeter said. "We don't have very many games left."
The Yankees had lost seven of 10 entering Wednesday night's game against the Rangers, who took the first two games of the four-game series. New York was 3 ½ games behind Boston in the AL wild-card race, with Texas only 1 ½ back of the Yankees.
Relief pitcher Chris Britton was called up from Triple-A Scranton/Wilkes-Barre to replace Chamberlain on the roster.
On Tuesday, Chamberlain flew back to New York and underwent a series of tests, including an MRI, at Columbia Presbyterian Hospital in Manhattan. He was then sent to see Andrews.