That's UFC champ, Kamaru Usman, telling TMZ Sports he TRIED to make a fight with Conor McGregor happen earlier this year ... but the Irishman was all talk.

"If Conor wants to put my name in his mouth, then come get some."

Kamaru is on a TEAR right now -- running through some of the top fighters in the welterweight division including Tyron Woodley AND Jorge Masvidal.

Conor -- who's won UFC titles at 145 lbs and 155 lbs -- has flirted with the idea of fighting for that 170 lb welterweight belt, but Kamaru says when push came to shove, Conor didn't want the smoke.

"[A Conor fight is] just a lost cause," Usman says ... "because we both know Conor -- the only time Conor gets up to the welterweight division is if he's able to pick and choose lightweights with double-digit losses that he can pick off and not have to cut weight to get down to lightweight."

"If Conor wants a piece at welterweight, he knows who the king of the division is. I'm not going anywhere! I'm right here!"

There was also talk about a possible Conor McGregor vs. Masvidal matchup down the line ... so we asked Usman who would win that fight.

"Honestly, I don't know and truthfully I don't really care. At this point in my career, I'm just worried about me."

Usman says his focus is on getting back into the Octagon and fighting the best in the world -- noting he's still hoping he can lure Georges St-Pierre out of retirement!