The 25-year-old singer took to Twitter in June to challenge the 57-year-old Hollywood actor to a fist fight - but Justin now admits it was a ridiculous idea.
Speaking to James Corden on 'Carpool Karaoke', Justin confessed: ''I don't know [what I was doing]. I was just being stupid, to be honest.
''[But] then people were like, 'I wanna see this happen.' And I was like, 'You know what? That could actually be funny.'''
James subsequently suggested the proposed fight wouldn't have been ''much fun'' for Justin.
The TV star explained: ''I gotta say, if you and me have a fight, you win. If you and Tom Cruise have a fight, I'd back Tom every day of the week.''
But Justin didn't agree with James' assessment of the proposed fight.
The 'Yummy' hitmaker replied: ''Absolutely not. I'm trying not to let my ego get in the way, but there's absolutely no way. He's not the guy you see in movies.''
James then reiterated his faith in Tom, hailing the actor's fitness levels.
In response, Justin quipped: ''I start to get frustrated. You're really boiling me up! I'm gonna f**kin' fight you, bro!''
Justin also likened himself to UFC star Conor McGregor, suggesting he's one of the toughest men in the entertainment business.
The pop star - who married model Hailey Bieber in 2018 - joked: ''I'm dangerous! My agility is insane ... I don't think you understand the mind control that I have!
''My mind control is another specimen. I'm different. I'm the Conner McGregor of entertainment!''
In his original tweet, the 'Love Yourself' singer gave no reason for wanting to fight Tom, but said he wanted to take him on in ''the octagon''.
He wrote: ''I wanna challenge Tom Cruise to fight in the octagon. Tom if you dont take this fight your scared and you will never live it down. Who is willing to put on the fight? @danawhite ? (sic)''
The Mifo O5 PROs are some of the most durable wireless earbuds on the market and we can't recommend them enough.
A feminist folk trio we can get behind.
For the opening night of his latest UK tour Frank Turner packed out Leas Cliff Hall for his first gig in Folkestone, playing a solo tour with no...
The Winter Gardens saw Blossoms in the Spring as the band brought their 2020 tour to the seaside to promote their third album, 'Foolish Loving...
You'd be surprised at how few women get to headline rock and metal festivals.
What's new in the music world this week?
The Long Goodbye is the scariest thing you'll watch this year.
With virtually the same blend of wit and idiocy as the 2001 original, this fashion-scene...
Though Derek and Hansel have left the world of fashion modelling behind them, a part...
Derek, Hansel and some other familiar faces are back in Zoolander 2! After offering their...
After a disastrous return to the fashion industry following his retirement, which almost ended in...
When Justin Bieber was discovered by Scooter Braun and Usher Raymond after performing his songs...
Clearly designed with his 12-year-old female fanbase in mind, this backstage myth-making doc wants to...