Gray (hamstring) threw a bullpen session Monday, Christopher Smith of MassLive.com reports.
Interim manager Chad Tracy said Tuesday that everything went well during Gray's first round of mound work since his placement on the IL and added that the plan is for the 36-year-old to build up volume during his next bullpen session. Gray will be eligible to return from the injured list May 6 and seems to be on track to return on or shortly after that date.