BALTIMORE -- An MRI administered to Red Sox outfielder Cody Ross in Boston showed a small fracture in the outfielder's left foot, manager Bobby Valentine said Monday.

General manager Ben Cherington later put a loose timeframe on Ross's absence at six to eight weeks.

The fracture is in the navicular bone, which is the same bone that Dustin Pedroia fractured on June 25, 2010. Pedroia eventually required surgery after an aborted comeback effort and missed a total of 85 games.

Ross, who was injured fouling a ball off the foot in his last at-bat Friday night, was en route back to Baltimore to join the team in time for Monday night's game, and according to the manager will be available to pinch hit. "He said he has one more hit left in him,'' Valentine said. That could just be gamesmanship, though, given the risks involved.

Initial X-rays were negative, Valentine said, but Ross had been sent back to Boston for additional testing when he complained of continued pain.

Ross is expected to be placed on the disabled list Tuesday, when infielder Kevin Youkilis is expected to be activated, though Valentine did not confirm the DL move. "These things have a way of working themselves out,'' he said.

Ross would become the sixth Red Sox outfielder to be placed on the disabled list, joining Carl Crawford, Jacoby Ellsbury, Ryan Kalish, Jason Repko and Darnell McDonald. "Is that all?'' Valentine said facetiously.

The Red Sox also will be without outfielder Ryan Sweeney Monday night. Sweeney, who did not play Sunday because of what he called a "mild concussion," was undergoing additional MLB-mandated concussion testing. Valentine said he was awaiting the results of those tests, but said he elected to keep Sweeney out Monday night after trainers told him the outfielder felt some fatigue after taking swings in the cage.

Sweeney was injured making a diving catch Saturday night in Philadelphia, when he said he experienced a whiplash-like jolt to his neck.

For the latest on Ross's injury, click here.