Washington Nationals closer Sean Doolittle (knee) said he expects to go on a rehab assignment with Single-A Potomac on Friday. Doolittle threw a successful simulated inning this week but feels his mechanics and pitches need a little more work. The left-hander might only make one appearance with Potomac on Friday before being activated from the injured list when rosters expand on Sunday. He last pitched on Aug. 17 and was really struggling before landing on the shelf, so his fantasy owners are ...