New England Patriots quarterback Cam Newton said on Monday that his poor play since returning to action from a bout with COVID-19 has nothing to do with a lingering "fog" related to the novel coronavirus.

"No, my goodness," Newton told WEEI 93.7's Greg Hill Show. "I'm hearing a lot of 'What could it be?' It's simple - I have to play better."

The 31-year-old Newton struggled mightily during Sunday's 33-7 loss to the San Francisco 49ers. He threw for 98 yards on 9-for-15 passing and three interceptions before being benched in favour of Jarrett Stidham.

While Patriots head coach Bill Belichick said in his postgame remarks that Newton remains his starter, the Auburn product says the early exit on Sunday was embarrassing.

"For any type of competitor, do you feel embarrassed? Yeah," Newton said. "The first thing I said to myself coming home was 'You keep playing games like that, bro, and it's going to be a permanent change."

The Patriots (2-4) are next in action on Sunday when they travel to Western New York to take on the AFC East-leading Buffalo Bills (5-2).