Kemp, 29, played only 73 games in 2013 because of ankle, shoulder and hamstring problems. He had surgery to repair his labrum during the 2012-13 offseason, then another clean up procedure this winter. The ankle procedure was to clean out loose bodies and deal with a bone spur.
The minor league season just started on Thursday, so Kemp did not play in any rehab games. He has been playing in extended spring training games instead. Kemp hit .270/.328/.395 (105 OPS+) with six home runs and nine steals around the injuries in 2013, but his performance was MVP caliber in 2011 (172 OPS+) and 2012 (147 OPS+).
To make room on the roster, outfielder Mike Baxter was optioned to Triple-A. It's unclear when Kemp will return to the starting lineup, but it figures to be soon. Otherwise they wouldn't have activated him.