Slaten (oblique) threw a bullpen session Monday, Christopher Smith of MassLive.com reports.
Monday marked the first time that Slaten has done any kind of mound work since he landed on the injured list in early April with a right oblique strain. Interim manager Chad Tracy said the right-hander is due to throw another bullpen within the next several days, after which the team will evaluate his progress and potentially determine when he may come back from the IL.