On Monday, Los Angeles Chargers head coach Anthony Lynn announced Philip Rivers has been placed in the NFL’s concussion protocol.

He said he doesn’t know when Rivers was injured and that he found out about it on Monday morning. Lynn also said Kellen Clemens will play Sunday against the Buffalo Bills if Rivers isn’t cleared to play.

Rivers played the entire game Sunday against the Jacksonville Jaguars, which extended into overtime. He completed 21-of-37 passes in the game — a 20-17 loss — for 235 yards with two touchdowns and one interception.

The Chargers dropped to 3-6 on the season with the loss and are tied with the Denver Broncos at the bottom of the AFC West.