According to Tom Pelissero of the NFL Network, "optimistic" early reports are he suffered a sprained ankle with some swelling and will undergo more tests.
Mixon had just 10 rushing yards on six carries before exiting in the second half of an eventual 21-20 loss. He added two catches for seven yards and was replaced by Giovani Bernard.
The third-year running back missed two games in each of his first two seasons and was limited by knee, wrist and thigh issues in 2018.
The 22-year-old is still coming off a breakout season when he totaled 1,168 rushing yards and eight touchdowns to go with 296 receiving yards. Expectations were even higher for 2019 as Mixon is one of the few clear-cut No. 1 running backs on his team.
The Bengals offense will lack elite explosiveness with Mixon out of the lineup. Bernard has always been a fine backup or guy in a timeshare but has never shown an ability to have elite performance with a full workload.