Bryce Harper isn't sure he can begin a rehab assignment as soon as Davey Johnson believes.

Johnson said Friday that he expects Harper to start a rehab stint Tuesday at Class A Potomac.

Harper, who has been sidelined with left knee bursitis since late May, said he thought he needed an extra day or two.

"It just depends how I feel today and tomorrow," Harper said. "Monday is an off day, which is good. Tuesday, that's kind of early. I'm thinking Wednesday or Thursday, maybe."