In a bizarre tweet Sunday night, Bieber challenged Cruise writing, "I wanna challenge Tom Cruise to fight in the octagon. Tom if you don't take this fight, you're scared and you will never live it down. Who is willing to put in on the fight?"
Then former UFC champion Conor McGregor chimed in supporting the challenge.
"If Tom Cruise is man enough to accept this challenge, McGregor Sports and Entertainment will host the bout," McGregor tweeted. "Does Cruise have the sprouts to fight, like he does in the movies?"
Just in case you're curious how the two match up, here's a breakdown, courtesy of Jake Marsh of the "Pardon My Take" comedy-sports podcast:
The 25-year-old pop star didn't elaborate about his tweet, but Cruise has yet to respond.
Meanwhile, social media had a little fun with this. Let's just say there weren't many who thought Bieber could win.
Here are some of the reactions:
Theodore Buttons: I think Tom cruise may be able to mess Bieber up
AJ Johnson: Dude, I think my 16 year old daughter might mess Justin Bieber up!
Anthony Fowler: He's 56 years of age you know lad?
Chuck Bush: I wanna challenge him not to.