Los Angeles Rams quarterback Matthew Stafford has been ruled out of Sunday’s game against the Kansas City Chiefs and is in concussion protocol, according to the Los Angeles Times.

Stafford left last week’s loss to the New Orleans Saints early after taking a sack, which prompted the team to evaluate him for a concussion. He said he felt numbness in his legs during that game, which came a week after he missed a game due to a concussion.

Rams coach Sean McVay said Wednesday that while Stafford is in concussion protocol, he has not been diagnosed with a concussion. He was ruled out officially due to a neck issue.

It’s unclear who will start on Sunday in Stafford’s place. The team is expected to give backup Bryce Perkins first-team reps this week leading up to the game, per the NFL Network’s Ian Rapoport. Perkins replaced Stafford against the Saints, and took over against the Arizona Cardinals two weeks ago. Fellow backup John Wolford missed last week with a neck injury he sustained against the Cardinals.

Perkins, 25, went 5-of-10 for 64 yards against the Saints, which marked the Rams’ fourth-straight loss. The Chiefs are coming off a 30-27 win over the Los Angeles Chargers last week, which was their fourth straight win.