Gsellman (triceps) threw a bullpen session Sunday and will throw another sometime over the next few days, Mike Puma of the New York Post reports.
Gsellman has felt strong throughout his rehab so far, and according to Puma, he's "very" optimistic that he'll be able to come back before the season concludes. The right-hander was placed on the injured list in mid-August with a partially torn right triceps.