The Eagles announced Sunday that they placed Ajayi on injured reserve with a knee injury. Multiple media outlets reported Ajayi suffered a torn ACL, which would be a season-ending injury.
Ajayi questioned the reduced role of the running game after Sunday's loss to the Minnesota Vikings, but he will not be a factor after suffering the injury against the Vikings.
He had eight carries for 29 yards and a fumble on Sunday and has 184 rushing yards for the season.
Ajayi's roster spot was filled by defensive tackle T.Y. McGill, who was claimed off waivers from the Los Angeles Chargers.
The loss of Ajayi, who becomes a free agent after this season, is another major blow for a team that has struggled to score points in its first five games. The Eagles have scored fewer than 24 points in each of their games.
Receivers Mike Wallace (fractured leg) and Mack Hollins (groin) were placed on injured reserve earlier in the season, and running backs Darren Sproles (hamstring) and Corey Clement (quadriceps) have been sidelined periodically.
"Obviously we want to be able to run the ball early and start that rhythm early in the beginning of the game," Eagles head coach Doug Pederson said Monday. "If I remember correctly, we had maybe three carries at the end of the first quarter."