Conor McGregor's got TWO Mayweathers threatening to beat his ass -- with Floyd's famous father vowing to knock out the UFC superstar himself ... for a fraction of the price!

64-year-old Floyd Mayweather Sr. -- who was a pretty good pro fighter himself -- put it very bluntly, "I'LL PUT HIS ASS TO SLEEP!'

Floyd's dad unloaded on McGregor to FightHype.com -- spelling out exactly why "Notorious" would get crushed in a fight where he wasn't allowed to use his "damn feet."

http://www.tmz.com/2016/11/21/floyd-...knock-him-out/