Kovalev's been getting heat for a meme he posted to his social media recently, one that depicts a fake convo between him and Ward, where Andre repeatedly uses both the N- and F- words.

Sergey has since deleted the video meme, but the backlash was swift from those who said that making it sound as if Ward -- a devout Christian -- dropped nonstop n-bombs was racist.

BTW ... it's not the first time the Russian fighter has been accused of racism, but he has said in the past that cultural misunderstandings were to blame for the controversies.

Ward ain't buying it, and told us there was NO DOUBT the post was racist, and he's gonna make Kovalev pay for it.

"He's culturally sound enough to know some of the things he's been doing are racially motivated. It's more motivation, definitely more motivation," Ward says ... adding, "He needs to be silenced."

** HERE'S KOVALEV'S VIDEO -- WARNING: CONTAINS OFFENSIVE LANGUAGE**