Clarke (hamstring) went 0-for-2 with a strikeout with Triple-A Las Vegas on Tuesday.
Clarke began his rehab assignment for a left hamstring strain, going hitless at the plate while logging five innings defensively in center field. The Athletics plan to build up the 26-year-old on a spring training-like progression, per MLB.com, so he's likely to see extended reps in Triple-A before being activated from the 60-day injured list. Clarke has appeared in 22 big-league games this season, slashing .170/.228/.189 with no homers, six RBI, four runs and two stolen bases.