WBO middleweight champion Billy Joe Saunders, who failed a doping test in August, has been denied a licence by the Massachusetts State Athletic Commission to face American Demetrius Andrade in Boston this month.
Saunders had tested positive for oxilofrine in a Voluntary Anti-Doping Association test (VADA). The stimulant is banned by VADA while it is prohibited only during competition by World Anti-Doping Agency and UK Anti-Doping.
Some reports suggested that 29-year-old Saunders had sworn at MSAC officials upon hearing the news.
He could be stripped of the belt he won from Andy Lee in 2015 if he fails to get a licence for his scheduled title defence on 20 October. He has the right to appeal the MSAC decision.
Saunders has denied any wrongdoing in the matter and said that the adverse analytical finding was the result of using a common decongestant nasal spray.
Warren insisted last month that the British Boxing Board of Control had "confirmed that Mr Saunders is not in breach of BBBofC or UKAD anti-doping regulations and is therefore in good standing and is licensed to box and defend his world title on 20 October."
Last month, Saunders was fined £100,000 by the BBBofC and given a severe reprimand about his future conduct after video footage emerged of him appearing to offer a woman drugs.