BOSTON — Red Sox outfielder Jacoby Ellsbury has hairline fractures in four ribs and it's uncertain when he'll be able to return.

Ellsbury has been out since April 11, when he collided with third baseman Adrian Beltre in Kansas City. Boston's speedy leadoff hitter would have been eligible to come off the disabled list Tuesday.

Dr. Thomas Gill told reporters on a conference call Thursday that Ellsbury's return will depend on how he feels.

"We keep people out of competition until there is no tenderness, don't have problems breathing and there is no stress," Gill said. "(It's) strictly symptom-based — these injuries are based on how long the symptoms last. As soon as he can swing, run, field and do everything he is supposed to do — he can return."

Ellsbury was moved from center field to left this season. His replacement in center, Mike Cameron, also is on the disabled list.

Ellsbury has played in six games this year. He has 10 hits in 30 at-bats, with two stolen bases.