He questioned whether Hollywood legend Cruise had the "sprouts" to take the fight against music heartthrob Bieber.
Speaking directly to Dana White, the president of UFC, he said: "Who is willing to put on the fight?".
Clearly, the week's off to a grand start when one wakes up and hears that Justin Bieber challenged Tom Cruise to a UFC fight. He might think a celebrity boxing match is rather silly or beneath him, for instance. Or perhaps he realizes that his best outcome from this is simply beating up Justin Bieber which is something he probably didn't wake up Monday morning wanting to do anyway.
And that's probably just as well, considering the response from his Twitter followers.
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Reps for the stars did not immediately return PEOPLE's request for comment.
Some stats: "Bieber is 25 years old, 5'9", and reportedly 146 pounds. Yes, you read that correctly.
It's unclear just what beef (if any) Bieber has with the Top Gun actor, 56, but Cruise is known for his athletic prowess, often completing his own death-defying stunts on his film sets.
In other words: This is Cruise's mission, should he choose to accept it.