He didn't practice Wednesday and was limited Thursday and Friday before the team officially listed him as out.
Thomas has only played one game in 2020, catching three passes for 17 yards.
It has otherwise been a disappointing season for the 27-year-old, who has missed time because of a high-ankle sprain and Grade 1 hamstring strain. He was also inactive for his team's Week 5 game against the Los Angeles Chargers after an altercation with a teammate.
These problems are new for a player who had been one of the most reliable receivers in the NFL entering the season.
Thomas had played 63 of 64 possible regular-season games in his first four seasons, finishing each year with at least 90 catches and 1,100 receiving yards. He set an NFL record in 2019 with 149 receptions while also leading the league with 1,725 yards on his way to the Offensive Player of the Year award.
The three-time Pro Bowler hasn't been able to replicate this type of production in 2020 and has barely even seen the field.
Drew Brees has helped keep the passing attack afloat with Thomas on the sidelines, although the team is thin at receiver with inexperienced players such as Tre'Quan Smith, Marquez Callaway and Deonte Harris taking on bigger roles.
The team will need more of the same going forward to keep winning in a competitive NFC South.