UFC's Donald Cerrone Rocks 'Red Dead Redemption 2' Outfit for Fight Week

UFC star Donald "Cowboy" Cerrone is so obsessed with "Red Dead Redemption 2" -- he's even dressing like the characters for a little fight week inspiration.

Cerrone is fighting "Platinum" Mike Perry at UFC Fight Night 139 in Denver on Saturday -- and if he seems extra violent this week, it's because he's been murdering everyone in New Hanover.

Cowboy doesn't even consider himself a "gamer" -- but said he HAD to buy 'RDR2' because it seemed to be right up his alley ... and he was right.

The game is already a massive hit -- earning a record $750 MILLION in the first 3 days of sales. In fact, one of the plot points in this week's "South Park" episode is how everyone is obsessed with the game.

Right before we started the interview with Cerrone, he told us his outfit was inspired by Arthur Morgan -- the main character in the game.

"Not only have I been playing the game, but I pre-purchased the $100 package with the horses and the guns."

"It's Cowboy all the way. So, I love it. Yeah. It's so cool. Just how you can just kill everybody. Whatever you want. I can't go into any town without being harassed by everyone, 'cause I just murder everybody."