In what would be one of the strangest Hollywood showdowns in history, Bieber, 25, challenged the 56-year-old actor to a bout, boldly claiming the "Mission: Impossible" star would "never live it down" if he denied the match. Tom if you don't take this fight your scared and you will never live it down.
Bieber wrote: "I wanna challenge Tom Cruise to fight in the octagon".
UFC star Conor McGregor responded to Bieber's message by offering to host the fight.More news: Girish Karnad: Veteran actor dies at 81
He concluded his post by tagging Dana White, the head of the UFC (United Fighting Championship), writing: "Who is willing to put on the fight?".
"Does Cruise have the sprouts to fight, like he does in the movies?", asked the Irish sportsman on Twitter.
As if that weren't enough, McGregor then used the opportunity to up the ante even more, sending a follow-up tweet with a proposal for his own fight - against Mark Wahlberg.
In a further twist, McGregor seemingly challenged actor Mark Wahlberg on the same card.More news: Bruins trounce Blues to send Stanley Cup Final to Game Seven
Yet most seem to think Cruise - who regularly trains to stay in peak physical condition and does many of his own stunts in his films - would wipe the floor with the "Baby" singer.
Boxer Oscar De La Hoya also offered up Golden Boy Promotions, his combat sport promotional firm, to help get the fight going.
"Just for the record, Bieber stands 5' 9", while Cruise comes in just below that at 5' 7".More news: Protesters in Kazakhstan dispute legitimacy of early presidential election