Henry Cejudo says he's "dumbfounded" that Conor McGregor thinks he deserves a rematch with Khabib Nurmagomedov ... telling TMZ Sports the guy needs to shut up and fight Justin Gaethje to prove he's worthy!
The UFC's reigning flyweight and bantamweight champ went off on Conor -- WITH JUSTIN -- saying McGregor is a bad guy who doesn't deserve a title shot without going through a quality opponent first.
And Henry thinks Gaethje is the PERFECT dance partner.
"Yeah, that man likes to sucker punch the elderly," Cejudo says about McGregor .