Former Highlanders captain Nasi Manu. Photo: Getty Images
Manu, now playing for Italian club Benetton, has been out for the last few months with what was initially described as an unspecified accident.
But a tumour was found and operated on at the end of August.
He was discharged for a period of convalescence, but earlier this week had further medical checks and blood tests which highlighted the need to start a chemo cycle.
Manu says it's put things into perspective and he's urged his fans on Twitter, to not be embarrassed and "check your balls".