The Eskimos updated Reilly's status Sunday after he left Saturday's game against Toronto in the fourth quarter.
The Eskimos said Reilly will undergo tests this week to determine the extent of the injury.
Reilly completed 16 of 28 passing for 170 yards, a touchdown and an interception against Toronto before being replaced by backup Matt Nichols with about three minutes to go in the game.
Reilly was a big part of Edmonton's resurgent 2014 season. He threw for 3,327 yards and 16 touchdowns and rushed for 616 yards and eight TDs as he helped Edmonton to a 12-6 record and a spot in the CFL Western final, where the Eskimos lost to the Grey Cup champion Calgary Stampeders.