Coach Bobby Petrino said the injury was likely caused during Coleman's rehab following a procedure to repair his torn right quadriceps in late April.
Doctors drained blood from Coleman's leg on Thursday. Further exams showed loose debris in his knee, which required surgery.
Since the start of 2003, Coleman's 44.5 sacks lead NFL defensive tackles. The Falcons signed Coleman to a six-year contract in March '04 that included $10 million in guaranteed bonuses. He has missed just one start since Week 9 of his first year with Atlanta.
When the Falcons open the season on Sunday at Minnesota, Jonathan Babineaux will start in Coleman's spot alongside nose tackle Grady Jackson and right end John Abraham.
Jackson did not practice on Friday because of back spasms, but Petrino believes he will be ready to face the Vikings.
The Falcons also signed quarterback Casey Bramlet from the practice squad, clearing room on the 53-man roster by releasing nose tackle Remi Ayodele.
Bramlet will dress as the No. 3 emergency quarterback behind starter Joey Harrington and backup Chris Redman.
Rookie Trey Lewis, a sixth-round draft pick from Washburn University, will work as the primary reserve behind Jackson and Babineaux on Sunday.
Copyright 2007 by The Associated Press. All Rights Reserved.