Forget Conor McGregor ... UFC fighter Kevin Lee wants to throw down with Kamaru Usman next -- telling TMZ Sports he thinks that scrap would be WAY more challenging than one with The Notorious.
"He might not bring the attention and the money," Lee says ... "But as a competitor, he'll bring a lot more."
Of course, Lee has been trying to set up a fight with Conor and Khabib Nurmagomedov for the last year ... telling us in the past he'd beat both their asses.