Doolittle threw off a mound for the first time on Tuesday, throwing 21 pitches, reports John Shea of he San Francisco Chronicle. Doolittle is getting closer to a rehab assignment, but still will need a few more side sessions before that occurs. Assuming no setbacks, Doolittle is still likely to be back with the A's in late May. Once fully healthy, he will likely reclaim his role as the A's closer.