Josh Allen left his team's Week 4 game against the New England Patriots in the fourth quarter after taking a hard helmet-to-helmet hit from Jonathan Jones, and the Buffalo Bills are taking a cautious approach with their starting quarterback.

ESPN's Adam Schefter reported Sunday that Allen is in the concussion protocol.

Allen struggled against the Patriots before exiting. He completed just 13 of 28 pass attempts for 153 yards with zero touchdowns and three interceptions.

The Bills play the Tennessee Titans on the road in Week 5. If Allen is unable to play versus the Titans, backup quarterback Matt Barkley likely will get the start.

Barkley completed nine of 16 pass attempts for 127 yards and an interception after replacing Allen in Sunday's 16-10 loss to the Patriots

Kyle Van Noy has NSFW response to Pats' goal line stand>>>

Click here to download the new MyTeams App by NBC Sports! Receive comprehensive coverage of your teams and stream the Celtics easily on your device.