According to a statement by the Eagles, Vick failed Wednesday's ImPACT exam, which compares a player's current status to his baseline.
The exam is one of the final hurdles Vick needs to clear before he can return.
The team says Vick has made substantial progress since suffering a concussion in Week 10 against Dallas, and that he has been attending team meetings and taking part in throwing sessions.
Foles was set to take practice reps with the team on Thursday.
The Eagles say in three full games, Foles has completed 59.6 percent of his passes for 542 yards, with one touchdown against three interceptions.