Sonny Bill Williams wants to fight Mike Tyson, but only if it's for a good cause

The former All Black and Kiwis representative has been mentioned as a possible opponent for the former undisputed heavyweight boxing champion, who is believed to be keen on a come-back at the age of 53.

Williams told the Sydney Morning Herald that for a good cause it would be an honour and career highlight to share the ring with an iconic figure of world sport.

He says it would be a humbling and surreal moment to stare at Tyson and know he was facing one of the greats.