Mathews had to be helped off the field. After being examined on the bench, Mathews was taken to the locker room on a cart. He jogged back to the bench midway through the second quarter.
"I feel like I could have played, but they didn't want to risk it, so they sat me out," Mathews said.
Mathews was being tackled when Jaguars linebacker Kirk Morrison landed on his legs.
"Whether he could've or couldn't have returned, I wasn't comfortable having him return," coach Norv Turner said. "Depending on the severity of it, I don't want an injury that might be a one-week injury turn into a six-week injury."
In two games, Mathews has 101 yards on 24 carries, two fumbles and no touchdowns. The two fumbles have led to 10 points for San Diego's opponents, including a Jacksonville field goal Sunday.