British heavyweight Dillian Whyte is on the verge of losing his career after reportedly testing positive for banned substances before his bout with Oscar Rivas during the weekend.

The failed drug test will have the 31-year-old boxer face an eight-year ban if confirmed, because it would be his second time committing the offence. He served a two-year ban from 2012 to 2014 for unknowingly taking an illegal supplement.

Dillian Whyte is understood to have returned the positive test, which was conducted by UK Anti-Doping (UKAD), three days before his victorious fight against Colombian Oscar Rivas at The O2 on Saturday.

When testing agencies take blood or urine from athletes, they split it into A and B samples, with the latter being a smaller amount used for backup, reanalysis or verification purposes. When told about the initial positive, Whyte asked for his B sample to be tested, as is his right, which would not have been possible until this week. This meant Ukad, the sport’s governing body the British Boxing Board of Control (BBBofC), and the World Boxing Council’s chosen testing body the Voluntary Anti-Doping Agency (VADA) had little option but to allow him proceed with the fight.

The banned substances were confirmed to be epimethandienone and hydroxymethandienone, which are by-products of the body breaking down anabolic steroid dianabol.

Whyte’s promoter Eddie Hearn wrote in a tweet: “Further to reports I can confirm that both Dillian Whyte and Óscar Rivas were subject to extensive VADA and UKAD testing for their bout. Both fighters were cleared to fight by both bodies and the BBBofC.”