Simmons will exit the bubble for the surgery. A timetable for his return will likely be set following the procedure, according to Reynolds.
The Australian is unlikely to play again this season unless the Sixers makes a deep playoff run, sources told ESPN's Adrian Wojnarowski.
Simmons was initially ruled out indefinitely by the team after sustaining a subluxation of his left kneecap. He appeared to suffer the injury while securing a rebound during Wednesday's win over the Washington Wizards.
The 24-year-old is averaging 16.4 points, eight assists, and 7.8 rebounds in 57 games this season.