The pair – who became mates last year – trained together in a gym in the US, with Justin showing off his growing muscles.
The 20-year-old looked pretty professional when he was throwing jabs and ducking punches.
But he does seem a little slow. Practice makes perfect, eh?
Justin shared loads of photos from his training session with the world champion boxer, captioning one: “Me and the champ”.
For some it’s probably refreshing to see the* Baby* singer out of trouble for once.
The police were called to his Beverley Hills apartment twice this week due to noise complaints.
According to TMZ, in one evening neighbours called them to help break up a party of around 40 people.
Justin did as he was told though because he’s still on probation for that infamous egging incident.