For his first fight since the assault charge, McGregor took part in an exhibition bout against John Joe Nevin at Crumlin Boxing Club in Ireland last week.
McGregor has evidently been training hard for his UFC comeback. His shredded figure shocked followers on Instagram.
The former featherweight and lightweight champion posted the topless photo on Monday with the caption, "Who the fook is that guy?"
The buff fighter is seemingly taking advantage of the fact that he won't have to cut much weight for the welterweight fight.
McGregor has previously competed in the 170-pound division twice, going 1-1 with Nate Diaz in 2016.
Cardio was an issue for McGregor during the bouts against Diaz, and it could remain a problem when he faces Cerrone next month. McGregor's record is 21-4 in professional fights.