UFC 303 is in need of a new co-headliner after Khalil Rountree admitted to taking a banned substance ahead of the June 29 event.

In a statement on social media, the light heavyweight revealed that he inadvertently took a “blended supplement” that contained dehydroepiandrosterone (DHEA), an endogenous steroid hormone precursor. Rountree was scheduled to face former UFC champ Jamahal Hill at the T-Mobile Arena in Las Vegas. It is currently unknown if Hill will remain on the card against a replacement opponent.

“I’m gutted to deliver this news to you all, but I will not be fighting at UFC 303 due to consuming a banned substance. I did not do this intentionally, and I am doing everything I can to get this situation taken care of,” Rountree wrote on Instagram.

“I was using a personalized tailored supplement service from a company that I trusted who understood my limitations in what I can and cannot take. They accidentally sent a blended supplement to me that contained banned substance called DHEA (which is prohibited at all times under the UFC anti-doping policy). Only after I consumed was its ingredients brought to my attention.

“I immediately contacted senior vice president of anti-doping compliance Jeff Novitzky and UFC vice president of anti-doping compliance Donna Marcolini upon receiving that information to inform them of this matter. I’ve provided them with all of the information to show that this was not a matter of cheating or to enhance performance. Although DHEA is non-performance enhancing, it is a banned substance, therefore I am under temporary suspension.

“My sincerest apologies to you all and Jamahal for this unfortunate series of events. This is a huge loss and an even bigger lesson.”

Rountree has won his last five Octagon appearances. Most recently, the 34-year-old known as “The War Horse” defeated Anthony Smith via third-round TKO at UFC Fight Night 223 on Dec. 9.

If he remains on the card, Hill will be making a relatively quick turnaround after suffering a knockout loss to Alex Pereira in a light heavyweight title bout at UFC 300 on April 13.