Bynum, acquired by Philadelphia in a four-team trade before the season, has yet to play for the Sixers and spoke before a game against Utah.
He has been recovering from a bone bruise on his right knee, and his return has been pushed back three times since the beginning of training camp. The Sixers were hoping Bynum would be cleared to return to basketball activities by Dec. 10.
That date is now in question because of issues with his left knee. Bynum says he now has swelling and a bone bruise on both knees.
"I had a little bit of a setback," Bynum said. "Just working through some issues with the right knee, I kind of have a mirror thing going on with the left knee. I don't know what's going on. The doctors are saying it's a weakened cartilage state, so we kind of wait, I guess. We can't do anything. I just have to wait for the cartilage to get strong."
Bynum did say he targeted Dec. 10 as a possibility, with one to four weeks of basketball-related activity to follow, pushing his much-anticipated debut to anywhere from mid-to-late December to as late as mid-January.
"It's the same exact spot (as the right knee) with the cartilage," Bynum said. "Just doing routine things and it started swelling up. No blunt-force injury or anything like that. It's the same timetable still."
The Sixers entered Friday 4-4 without Bynum, including three straight losses at home.
Bynum announced in May, while still a member of the Los Angeles Lakers, that he was going to Germany in September for the Orthokine blood-spinning treatment in his knees that other professional athletes have sought. The Sixers announced before training camp that Bynum needed to delay his return to allow the effects of the Orthokine treatment to work.
The bone bruise in his right knee caused the Sixers to push the return date from training camp to the regular season and now possibly to midseason.
But the Sixers are still looking long term with Bynum, who's in the last year of his contract.
"My main concern is Andrew's health," Sixers general manager Tony DiLeo said. "My main concern is big picture. We want to have a long relationship with him."