Baker was injured during the fourth offensive series of the Falcons' preseason game against the Houston Texans on Saturday.
Baker, 29, played just four games last season after having surgery on his patellar tendon in his left knee. He signed a six-year, $41 million deal with Atlanta last offseason.
"Sam had worked extremely hard to get back on the field after missing most of last season, and he was having a good camp," Falcons head coach Mike Smith said. "I know he is disappointed, but I also know he is a very resilient football player and will do whatever he can to bounce back.”
Rookie Jake Matthews said he is willing and able to play left tackle.
"I'll do it," Matthews told ESPN.com. "That's what they drafted me for: to come here and play wherever."
- Scooby Axson