"After (Sunday's) game, he went to the doctors," coach Jim Caldwell said on Tuesday. "He was exhibiting some issues, they evaluated him and thus they had to put him in (protocol), which he's in today. You probably won't see him out at practice this afternoon."
Swanson also sustained a concussion with delayed symptoms last season against the New Orleans Saints on Dec. 4, 2016. The 26-year-old appeared on the injury report days later with a concussion and sat out the final four games of the season as well as the club's playoff game versus the Saints.
Should Swanson remain sidelined, left guard Graham Glasgow could be shuffled to center as the Lions (7-6) host the Chicago Bears (4-9) on Saturday at Ford Field.