"He'll take his test results with him," Yankees manager Joe Girardi said. "Until I hear from Dr. Andrews, that's all I've got."
Chamberlain was removed from Monday night's start against the Texas Rangers in the fifth inning with what the club announced was a stiff right shoulder.
On Tuesday, Chamberlain flew back to New York and underwent a series of tests, including an MRI, at Columbia Presbyterian Hospital in Manhattan.
The Yankees are already without No. 1 starter Chien-Ming Wang and right-hander Phil Hughes. Subtracting Chamberlain from the rotation would be a huge blow to the team's postseason chances.
"I think we're all hopeful," Girardi said. "I hope we don't miss him for very long. But you think of a guy of Joba's caliber and you know he's going to miss a start, that doesn't mean the guy who replaces him can't pitch well."
Girardi said the 22-year-old right-hander would probably miss his next turn in the rotation. Anything longer would be a setback for the injury-riddled Yankees pitching staff.
"I envision him not making his next start," Girardi said. "Beyond that, I can't say."
Girardi said his options for replacing Chamberlain include moving right-hander Darrell Rasner back into the rotation or recalling a pitcher from Triple-A Scranton.
Girardi said the Yankees will be cautious with Chamberlain, even in a close playoff race.
"You're always careful with your players," Girardi said. "You don't want to jeopardize their long-term health. And we're talking about a 22-year-old kid here."
