The Rams placed Long on injured reserve with the designation to return. Long can't practice with the Rams for at least six weeks, and can't play for at least eight weeks. Long is eligible to return for the Rams' Nov. 9 game in Arizona.
Long recorded 33 tackles and 8.5 sacks in 16 starts last season. The 29-year-old has amassed 50.5 sacks and 181 tackles over six-plus seasons.
The Rams, which fell 34-6 to the Vikings to open the season, play at Tampa Bay on Sunday.
- Chris Johnson and Sarah Barshop