It’s up in the air as to whether Ryan Mathews will play against the Oakland Raiders, but I doubt it.
Mathews should play if there’s little risk of re-injury. If there is, he should sit out until that risk is minimal.
In the first game of the season, the San Diego Chargers will be totally out of sync anyway. Not one time has a Norv Turner team built on a successful end of season run in San Diego.