Jarrell Miller's co-promoter Dmitriy Salita is disappointed by "shocking" reports that the American heavyweight has failed another drug test.
'Big Baby' Miller was due to return against Jerry Forrest in Las Vegas next month after signing a new co-promotional deal with Top Rank, but the New Yorker will now be placed on temporary suspension by the Nevada State Athletic Commission.
Salita is awaiting a final ruling from the NSAC on Miller, who tested positive for banned substances before his cancelled world title fight with Anthony Joshua last year.
In a statement, Salita told Sky Sports: "I am disappointed. I was looking forward to July 9th and Jarrell's return to the ring. This news is shocking to me as well.
"Hopefully soon we will find out more facts. As Bob Arum said, we're all going to be guided by the decision of the Nevada Athletic Commission."
Miller will be replaced by a new opponent, confirmed Top Rank's vice president of boxing operations, Carl Moretti.
"We are aware of the situation," Moretti told BoxingScene.
"He will be placed on temporary suspension by the Nevada State Athletic Commission on Monday morning. We are currently working on a replacement opponent for the main event on July 9th."
The unbeaten 31-year-old had set his sights on a fight with Tyson Fury as he aimed to propel himself back into world title contention.
Asked about a fight with Fury, a fellow Top Rank fighter, Miller told Sky Sports in April: "I think that they were talking about it after Fury fighting Wilder again.
"I was supposed to be the co-main event for that fight. I was supposed to be the co-main event for the last fight.
"I think that will be definitely in the future."