Foster did not endure ligament damage and will avoid surgery on the knee after injuring his knee during a padded training camp session at Saint Vincent College, per NFL Network's Aditi Kinkhabwala. The 32-year-old Foster, however, sustained a bone bruise and a stretch of the MCL.
Backup B.J. Finney will likely see additional reps in the absence of Foster, who held his right knee after going down on the third play during 11-man work on Saturday.
The four- to five-week timeline would leave Foster with a week or two to prepare for the Steelers' season opener against the Cleveland Browns on Sept. 9.
Foster, who was undrafted out of Tennessee in 2009, has started 115 of the 130 games he's played with the Steelers. He is in the final season of a three-year, $9.6 million contract.