Looking at this shoulders and muscles for McGregor I cant think of anything else but him using some kind of steroids.
Aside from Nate Diaz and GSP, Conor is also one of those guys who doesnt want to be juiced. I'm not ruling out the possibility though, let's wait for the test results after the fight.
I just watched a video from Masvidal's youtube channel, he and Usman is going to excite many fans if they decide to do it.