Vernon Wells, out since May 21 because of a torn ligament in his right thumb, is expected to begin a minor league rehabilitation assignment of seven to 10 games this weekend, moving a big step closer to a return that could cause tension in the Angels' clubhouse and test the patience of fans. Wells, who has been taking batting practice for a week and throwing for several weeks, was the starting left fielder when he was injured, but since then, outfielders Mike Trout, who joined the team April 28, and Mark Trumbo have emerged as most-valuable-player candidates.