UFC Champ Cain Velasquez -- Jon Bones Jones Should Beef Up for Superfight

UFC heavyweight champ Cain Velasquez says there's NO REASON why Jon "Bones" Jones can't put on the extra pounds to face him in a superfight for the title belt, TMZ Sports has learned.

We carefully approached Velasquez at LAX yesterday afternoon ... and he said Bones -- the reigning light heavyweight champ -- at 6'4' has what it takes to move up a class.

Cain said, "I think he has the body for it too ... he's tall so he can put on that weight."