UFC announced Friday that Junior Dos Santos has been informed of a potential violation of its anti-doping policy after the U.S. Anti-Doping Agency flagged an out-of-competition sample collected Aug. 10.
As a result, Dos Santos has been removed from his upcoming fight against Francis Ngannou at UFC 215 in Edmonton.
"We are still trying to understand the test results, so that we can investigate and determine what happened," dos Santos' manager, Ana Guedes, told ESPN.com's Brett Okamoto. "What we know as of now is that Junior dos Santos has never taken PED's, has never knowingly used any banned substances, and has always supported USADA's policies and efforts to keep the sport clean.
"If ever there was a fighter who made his position on this issue unequivocal, it's Junior. We are confident that we will be able to figure out what happened, and will provide an explanation once we have one."
UFC confirmed it is looking for a replacement to square off against Ngannou Sept. 9 at Rogers Place.
Ngannou tweeted his reaction to the news shortly after it became official:
According to MMA Fighting's Dave Doyle, Dos Santos (18-5) can't be sanctioned by UFC until he has a formal hearing.
It's been a rough few years for the former heavyweight titleholder.
Since failing to reclaim the strap from Cain Velasquez at UFC 166 in 2013, Dos Santos has lost two of his last four fights, including a first-round knockout at the hands of Stipe Miocic in May.
With Dos Santos off the card for next month's proceedings in Edmonton, Ngannou (10-1) will need to await word on his next opponent and adjust on the fly as he seeks to capture a 10th straight win.