Anthony Joshua believes Jarrell Miller does not deserve a fight against anyone after his failed drugs tests.
Miller was due to face WBA, IBF and WBO heavyweight champion Joshua in New York on June 1, only for promoter Eddie Hearn to reveal the American had failed two tests.
Joshua, who is 22-0 and set to fight outside United Kingdom for the first time, is hopeful a new opponent will be announced in the coming days.
The Brit said there was no way Miller deserved a fight after his failed tests.
"Just to say good luck to the kid Jarrell Miller whatever he does with his life," Joshua said in a video posted on his YouTube channel.
"As I said, I'm not going to knock you when he's down, but he doesn't even deserve to be in the ring with me or any other heavyweight right now.
"I don't know what the future holds – that's not up to me, that's up to the governing bodies. They'll make the right decision and right call in this situation."
Miller, also unbeaten and holding a 23-0-1 record, has since admitted he "messed up" after losing his title shot.
Joshua said Miller had annoyed him in the lead up to their scheduled bout, the Brit having passionately dismissed accusations of drug use made by the American.
"I didn't want to talk too much in the situation with Jarrell Miller because it's not in my character to knock a man when he's down," he said.
"However, there was a lot of things that he has said previously in the press conferences in the build-up [that] I wanted to crack him in his jaw. But I know when you're in that position, you have to lead by example and I knew that wasn't the right thing to do.
"The lesson to learn in this situation is karma works in various ways and what goes around will come back around and I feel like he has taken fate and his own blessings out of his own hands.
"Sometimes, be respectful. I know it's a fight, but be respectful, be appreciative and lead by example and what he had done is not leading by example."