Rookie Oakland Raiders linebacker Khalil Mack seems to be getting stronger as he prepares for his 15th game of the season.

Mack has flashed in recent weeks, getting all three of his sacks since Week 11. There has been no rookie wall for the No. 5 overall pick from Buffalo.

“It doesn’t seem to happen with him,” Oakland interim coach Tony Sparano said. “He’s been really steady and has gotten progressively better each week. That’s a guy who hasn’t hit the wall. He’s got a lot of gas left in his tank right now and it’s been good to watch.”

In other Raiders notes:

• Sparano said the coaches challenged the special teams unit to be better against a Buffalo Bills team that brought back a punt for a touchdown in Week 15. Oakland’s cover units have been awful this season. It hit bottom Sunday when the Kansas City Chiefs' De'Anthony Thomas returned a punt 81 yards for a touchdown.

• Oakland defensive coordinator Jason Tarver praised the play of young players, defensive tackle Ricky Lumpkin and linebacker Ray-Ray Armstrong at Kansas City. They are playing more because of injuries.

• The game is a sellout and will be shown on local television. All seven games in Oakland this season were declared sellouts. The Raiders also had a "home" game in London.