Mattison rushed nine times for 36 yards in the Raiders' 41-24 loss to the Bengals on Sunday.
Coach Antonio Pierce said Wednesday that Mattison will remain the starting RB, but Pierce also wants to get Zamir White more involved, Levi Edwards of the Raiders' official site reports.
Mattison is in line to lead the Raiders backfield Sunday against the Steelers with Zamir White (groin) inactive.
Mattison is set to operate as Vegas' top running back against the Broncos on Sunday, as Zamir White (groin) has been ruled out, Paul Gutierrez of ESPN.com reports.
Raiders head coach Antonio Pierce said Monday that Mattison's recent quality of play has earned him more work and that he's "going to get it," Adam Hill of the Las Vegas Review-Journal reports.
Mattison rushed four times for one yard and a touchdown in Sunday's 26-23 win over the Ravens.
Mattison rushed five times for 19 yards and caught four of six targets for 43 yards and a touchdown in Sunday's 22-10 loss to the Chargers.
As the coming season approaches, Mattison profiles as Zamir White's top backup at the running back position, Tashan Reed of The Athletic reports.
Mattison is in line to sign with the Raiders, Tom Pelissero of NFL Network reports.
The Vikings officially released Mattison on Monday.