Mathews, who sprained his right ankle last weekend against the Jacksonville Jaguars, is unlikely to play Sunday, the source said.
Mathews tested his right ankle on the treadmill and in some cutting exercises before practice, but he didn't participate in the session. He said the joint is sore and uncomfortable, but it won't stop him from playing if given the green light.
"I can play," Mathews said. "There's a difference between being hurt and being injured. I can play in pain. It may be a bit uncomfortable, but as long as my bone's not sticking through the skin, I'm good to go. But I know that it's the trainer's decision and I'll go along with whatever they decide."
Tolbert is coming off a strong performance against the Jaguars. The third-year veteran ran with a physical and aggressive style and recorded 82 rushing yards and two touchdowns on 16 carries.
The Associated Press contributed to this report.