American Claressa Shields is under investigation after testing positive for marijuana following her win over heavyweight Danielle Perkins on 3 February in Michigan.
The 29-year-old – who is a three-weight undisputed champion – has been suspended from fighting in the state by the Michigan Unarmed Combat Commission.
Shields tested positive after providing an “oral fluid sample” after the fight.
Marijuana is banned in-competition by the World Anti-Doping Agency (Wada).
American sprinter Sha’Carri Richardson missed the Tokyo Olympics in 2021 after receiving a one-month ban following a positive drugs test for marijuana.
The WBO, which is a sanctioning body and does not have the power to suspend boxers, has requested a “show notice” from Shields, asking her to explain herself, while the Michigan Commission has opened its own investigation into whether she should face disciplinary action.
“Ms Shields’ conduct as a licensed professional boxer constitutes an imminent threat to the integrity of professional boxing, the public interest, and the welfare and safety of professional athletes,” the Michigan Commission said.
Last week, Shields addressed rumours of a failed drugs test on social media, saying she was a “clean athlete”.
BBC Sport has contacted Shields for comment.
Under the WBC’s clean boxing programme, Shields and Perkins would have been subject to drug testing by the Voluntary Anti-Doping Agency (Vada).
Shields won gold at the Olympics aged 17 and has won titles in multiple weights as a professional boxer.
She is undefeated in 16 fights and was the first boxer, male or female, to win undisputed titles in three different weights in the four-belt era.
