The injury occurred during Sunday night's preseason loss to Seattle, and thins the Indianapolis backfield, while also eliminating a key special teams performer. Mungro, 28, will be placed on injured reserve. It is not yet certain when Mungro will undergo surgery to repair the damaged ligament.
In 43 games, including one start, Mungro rushed for 430 yards and 10 touchdowns on 133 carries. Most of his touchdowns came in short-yardage situations. He also has 24 receptions for 141 yards and three scores and 11 kickoff returns for a 14.3-yard average.
Perhaps the area in which Mungro's absence will be most felt is on special teams.
In an unrelated matter, the Colts have reached agreement in principle on a contract with wide receiver Marc Boerigter, who was released by the Green Bay Packers on Tuesday afternoon. Boerigter is expected to sign a one-year contract once he passes a physical exam.
The Colts are attempting to create some competition for the No. 4 wide receiver spot and, while Boerigter struggled in the Packers' camp, Indianapolis officials quickly contacted him after his release, feeling that he might be a good fit for their offense.
A four-year veteran, Boerigter is a tall, angular receiver (6-feet-3, 220 pounds), who once had outstanding deep speed for a big man, but who lost some of his quickness following 2004 knee surgery. He played four years with the Kansas City Chiefs before signing with the Packers as a free agent this spring.
Boerigter, 28, has only 39 career catches for 697 yards and eight touchdowns. But in 2002, he proved to be an effective "red zone" receiver, scoring eight times that season on only 20 receptions. He has appeared in 41 games with two starts.
Senior writer Len Pasquarelli covers the NFL for ESPN.com.