The Los Angeles Rams are uncertain when or if quarterback Matthew Stafford will return this season, league sources told ESPN.

Stafford is out Sunday against the Kansas City Chiefs because of a strained neck and two recent trips to concussion protocol. He suffered one concussion earlier this month, and the Rams never could prove he suffered a second concussion even though he was in the protocol a second time.

Stafford, 34, has absorbed plenty of physical punishment this season and the Rams on Wednesday ruled him out for their game against the Chiefs.

Rams coach Sean McVay said Stafford felt some numbness in his legs after taking a hit last Sunday against the Saints but also emphasized that even though Stafford is in the concussion protocol, it doesn't mean he has been diagnosed with a concussion.