Alexander Gustafsson is out of UFC 227 on Aug. 4 because of a minor undisclosed injury, his agent, Nima Safapour, said Sunday.
Safapour said the injury occurred last week.
"Since that time, we have been working closely with the UFC doctors, our doctors in Sweden, and the experts at the UFC Performance Institute," Safapour said. "We have been advised that Alex has a minor injury and he will not be permitted to compete at UFC 227."
"I'm very frustrated the last couple of days. I feel like it doesn't go my way," Gustafsson told ESPN.
"I'm in shape, I'm fit. I'll fight anyone, I'm telling you. But here we are. It is what it is. We had long talks, me and my team, and there's nothing more we can do," he said.
Safapour said Gustafsson was also prepared to face light heavyweight and heavyweight champion Daniel Cormier at heavyweight.
"Had Alex been fit to fight, we were prepared to face Rountree or anyone else the UFC had asked us, including [Cormier] at heavyweight," Safapour said. "Alex will be fighting again very soon. He will give his side of the story shortly. We don't care who the opponent is. But whomever we face it should be for the meaningful result of the [light heavyweight] UFC title."
Gustafsson (18-4), a former UFC light heavyweight title challenger, is coming off a fifth-round knockout of Glover Teixeira in May 2017.
A win at UFC 227 could have propelled him back in the light heavyweight title picture, quite possibly in a rematch with Cormier, who won their 2015 fight by split decision.