Carolina Panthers quarterback Cam Newton has been ruled out for Monday night’s game after suffering a concussion in last week’s loss to the Atlanta Falcons.

Newton has been under the league’s concussion protocol since last Sunday, when he went down following a helmet-to-helmet hit in the fourth quarter (deemed legal by the NFL). The protocol requires that a player gradually increase his activity before returning to playing, and Newton has sat out multiple practices this week while continuing to display post-concussion symptoms, according to The Charlotte Observer.

This week has not been the first time this season that Newton has been involved with concussion protocol—multiple helmet-to-helmet hits in the season opener, without any in-game examination, called for the NFL and the Players’ Association to investigate whether or not protocol had appropriately been followed for Newton.

Backup Derek Anderson will start for the 1-3 Panthers in Newton’s stead against the Tampa Bay Buccaneers on Monday night.