The UFC's most violent newcomer Justin Gaethje says he KNOWS a superfight with Conor McGregor is coming ... and tells TMZ Sports he'll beat the Irishman or die trying. 

The undefeated Gaethje made a helluva statement in his UFC debut last week -- stopping Michael Johnson in one of the most brutal/awesome fights ever. 

After the brawl, Gaethje called out Tony Ferguson -- and if he can get through Tony, it seems Conor McGregor could be waiting for him on the other side. 

Gaethje told the guys on the TMZ Sports TV show (airs tonight on FS1) -- "That's what I'm here for ... don't worry guys, you'll get to see it."

You gotta listen to Gaethje explain his fight mentality -- dude's no joke. 

Check out "TMZ Sports" weeknights on FS1.