An MRI this week revealed what the team termed a "slight" meniscus tear in Covington's right knee. No decision has been made on whether Covington will have surgery as he researches treatment options, a team spokesman said.
Okafor has dealt with intermittent right knee soreness since needing surgery for his own meniscus tear last March. He'd missed the previous four games with right knee soreness after it flared up during a game in Oklahoma City on March 22. He hasn't had an MRI.
Okafor averaged just 11.8 points and 4.8 rebounds in 50 games this season, losing playing time because of a logjam at the center position early in the season and then with knee issues.
"At this stage of the year, it seems like it's the right thing to do," Sixers coach Brett Brown said about the decision to shut Okafor down. "It's borderline zero doubt that this is the right thing to do.
"He had signs of fantastic play,'' Brown said. "He had signs of disappointment. I think to make any level of judgment is kind of grossly unfair because of the erratic nature of his health. There were times he was good to go and I chose not to play him when we had our abundance of centers. We look at some of those games he was able to get his touches, he scores. He scores in his sleep.''
Last week Sixers rookie Joel Embiid had surgery on his left knee to repair a meniscus injury. They've been plagued by injury issues including No.1 overall pick Ben Simmons out for the season with a foot injury.
Covington started having problems with the knee several weeks ago and missed a game against the Los Angeles Lakers on March 12 before returning and playing eight more games being shutting it down. He averaged 12.9 points and 6.5 rebounds in 67 games this season.
"Robert, by all standards, had his best year in the NBA,'' Brown said of Covington. "He grew to a level that was respected around the league as a legitimate two-way player.''
Brown said that under the circumstances, the team would be looking to add a player in the near future. The Sixers have a full roster but they are in position to apply for a hardship exception from the NBA to add a player because they now have four players out for the season.
The Associated Press contributed to this report.