Simmons will have a loose body removed from his left knee in the coming days, the team announced Saturday.
Only a deep Sixers playoff run could keep a fleeting hope of his return alive this season, sources said. Even then, his return from the procedure -- expected to take place outside of the Disney campus in the coming days -- is largely expected to come next season. The Sixers are preparing now for a postseason run that will come without Simmons, one of the league's most talented and versatile weapons.
The loose body was a result of a left patella subluxation suffered in Wednesday's victory over the Washington Wizards. A subluxation of the patella means that the kneecap popped out of place but returned on its own.
The Sixers had moved Simmons to the power forward spot, and now the team's offensive focus turns fully to All-Star center Joel Embiid. The Sixers will suffer significantly on the defensive end without Simmons, and offensively they'll count on a lineup of shooting surrounding Embiid that could give him more room to operate around the basket.
The injury also means the return of Al Horford in Philadelphia's starting lineup. Horford had been replaced in the starting five by guard Shake Milton when Simmons was shifted to power forward after the Sixers arrived in Orlando, but now is back starting next to Embiid.
The Sixers have struggled to maximize the talents of both big men when they have shared the court together since signing Horford as a free agent last summer. That has led Brown to try to limit the amount of time they were going to play together moving forward. Now he has little choice but to try to make it work.
Horford started next to Embiid and played quite well in Philadelphia's 108-101 win over the Orlando Magic on Friday, finishing with 21 points and nine rebounds in 30 minutes.
"We need [Horford] more than we've ever needed him," Brown said afterward.
ESPN's Tim Bontemps contributed to this report.