Jason Kipnis (who has been out since April 29 with a strained right oblique) will begin a rehab assignment with Triple-A Columbus on Friday.
The tentative plan is to have him play in that night's game, and then again Saturday night. He'll then sit out on Sunday, and visit with doctors to assess his status. If he feels good and is given medical clearance, he'll rejoin the team in Chicago for the start of the series against the White Sox (that could be ideal timing, given that Kipnis has hit especially well in Chicago throughout his career, with an 1.173 OPS in 104 plate appearances).
I would guess Justin Sellers is the man sent down at that time.
Kipnis was off to a mixed start before the injury. His defense was very shaky, and batting average was only .234, but that was due in part to a .245 BABIP, far below his career figure of .311. Meanwhile, his walk rate was up, his strikeout rate was down, and his isolated power was basically the same as a year ago. Mike Aviles has filled in admirably (with a .747 OPS since the injury), but Kipnis was the Tribe's best player in 2013, and it will be good to have him back in the lineup.