After Wilder told Tyson Fury that black people have been fighting in this country for 400 years -- he went off on a radio host who asked him to explain the comment.

Wilder exploded with a passionate rant about how black people have been oppressed and mistreated in the U.S. -- and he was offended that the radio host pushed him on the topic.

But, undefeated boxing star Jarrell "Big Baby" Miller has a problem with Wilder ... claiming he undermined his own message by meeting with President Trump back in May.

Wilder had visited Trump's White House with Sylvester Stallone and others as part of the group paying homage to Jack Johnson ... after President Trump pardoned the late boxer for a 1913 conviction many believe was racially motivated.

Miller -- a legit Top 5 heavyweight contender who's lined up to fight either Wilder or Anthony Joshua this year -- says Wilder got used by Trump to curry favor with African Americans ... and it's a stain on his public image.

"LeBron James, Steph Curry, a lot of other guys didn't want to go up to the White House because they knew what Trump was doing was just using black athletes as a shade to hopefully get black voters to get on his good side."

Miller sees this as Deontay talking out of both sides of his mouth and, although he loved Thursday's rant, he's got a message for Deontay when it comes to racial issues.

"We have to have the same energy all the time."