Jon Jones, the Ultimate Fighting Championship’s light-heavyweight champion and perhaps the top pound-for-pound fighter in mixed martial arts, is once again facing the prospect of his career being derailed by a positive drug test. If the test result, announced late Tuesday, is substantiated, he might not return to the octagon for a long time — if ever.
According to a spokeswoman for the United States Anti-Doping Agency, Jones “has been notified of a potential antidoping policy violation stemming from an in-competition sample” collected the day before his title bout against Daniel Cormier at U.F.C. 214 last month. The U.F.C. confirmedin a statement that it had been informed by Usada of the potential violation earlier on Tuesday.
A statement attributed to Jones’s manager, Malki Kawa, said that “Jon, his trainers, his nutritionists and his entire camp have worked tirelessly and meticulously the past 12 months to avoid this exact situation.” The statement also said that they would have his samples tested again.
TMZ, which first reported the potential violation, said Jones had tested positive for the steroid turinabol. The fight in July was his first after he returned from a one-year suspension by Usada for a previous positive test for banned substances.
Jones, 30, can ask for his “B” sample to be tested; he can also appeal any Usada decision.
If Jones’s latest positive test is confirmed, he will probably be stripped of his belt and, as a second-time offender, he will face up to a four-year suspension.
At a news conference at the U.F.C.’s primary training center in Las Vegas, the organization’s president, Dana White, called the news “unbelievable.”
If Jones is suspended for two to three years, White said, “it might be the end of his career. So to talk about his legacy — it’s probably the end of his career.”
Jones first won the U.F.C.’s light-heavyweight championship in 2011. He successfully defended his belt eight times — the last of those fights was against Cormier in 2015. Four months later, the U.F.C. stripped Jones of his title after he was arrested in a hit-and-run accident and charged with a felony. He later pleaded guilty and was sentenced to probation.
Jones then won the interim light-heavyweight championship, and a rematch against Cormier was scheduled for U.F.C. 200 in July 2016. The bout was canceled after Usada announced a potential doping violation.
Jones tested positive for banned substances clomiphene and letrozole and was suspended for a year. Users of anabolic steroids sometimes take both drugs as part of a doping cycle. Jones appealed his suspension, blaming the positive test on a male-enhancement pill he took, but an independent arbitration panel upheld the suspension.
Jones defeated Cormier at U.F.C. 214 in Anaheim, Calif., last month, in a third-round knockout. Jones knocked Cormier to the ground with a kick to the head, and he landed a number of punches before the fight was stopped.
Before that fight, Jones mocked Cormier on social media about previous steroid allegations, writing in one message, “Daniel says the only reason I defeated him the first time is because I must have been on steroids, wonder what his excuse will be this time.”
The California State Athletic Commission, which sanctioned the fight, also has jurisdiction over the matter. In a statement, Andy Foster, the commission’s chief executive, said it “takes these matters very seriously and will take any appropriate actions necessary after a thorough review of the situation.”
Jones “is entitled to due process,” he added.