UFC Champ Eddie Alvarez: Careful, McGregor, WWE Stars Are 'Incredible Athletes'

UFC lightweight champ Eddie Alvarez seems to be issuing a warning to Conor McGregor -- careful with the WWE smack talk ... 'cause a lot of those dudes are the REAL DEAL.

Of course, McGregor said WWE superstars are nothing but a bunch of "messed up p**sies" -- which pissed a lot of 'em off.

Now, Alvarez is sort of defending the WWE -- while making it clear what they do is an "act" ... he still acknowledges that a lot of 'em are "incredible athletes" who come from a real combat sports background.