Freeman suffered the injury during Atlanta's 18-12 loss against the Philadelphia Eagles on Sept. 6. He had just six carries for 36 yards in that game.
Falcons head coach Dan Quinn told reporters Freeman's injury is to the same knee that was injured at the end of last season, according to ESPN.com's Vaughn McClure. The fifth-year star played through PCL and MCL issues in Atlanta's two postseason games against the Los Angeles Rams and Eagles.
Atlanta is heading into Week 2 with a depleted roster. Safety Keanu Neal and linebacker Deion Jones are on injured reserve, with Neal expected to miss the rest of the season.
With Freeman sidelined, the Falcons will start Tevin Coleman in the backfield. Coleman had 45 yards from scrimmage against the Eagles last week and ran for a career-high 628 yards in 2017.