Richardson appeared at practice over the weekend with a walking boot on his foot. He missed all of the 2013-14 season after having left knee surgery in February 2013. He only played in 33 games in 2012-13.
Richardson, 33, is in the final year of his contract, and is scheduled to make $6.6 million.
"He is busting his tail to get back in shape and play again," 76ers head coach Brett Brown said. "He is not going down easy. He is not going to retire easily. He continues to work, to try and get ready. It is a setback."
The Sixers are also awaiting the availability of rookie forward Jerami Grant, who missed the entire preseason with an ankle injury, and Rookie of the Year Michael Carter-Williams, who is targeting to return to practice next week after having offseason shoulder surgery.
The 76ers start the regular season on the road on Wednesday against the Indiana Pacers.
- Scooby Axson