ALAMEDA – Raiders offensive coordinator Greg Knapp strode to the podium after practice Thursday and didn't wait for questions to deliver the theme of his comments to reporters: Yes, the offense has struggled, averaging 13.5 points in two losses and ranking 31st in the league in rushing.

But Knapp urged "patience."

"Let's keep things in perspective for a second here," Knapp said. "We've played two games in the regular season on offense. We've had two different centers and a right tackle who played half a game last week. We need some patience.

"You can't develop a scheme in two weeks in a regular season, especially when last week we faced the No. 3-ranked rush defense (Miami) from 2011 and the week before they held the No. 2 rush offense in the league (Houston) to 2.4 yards per carry. That was a good team we faced last week. The scheme will be fine. It just takes some time."

The Dolphins last week and the Chargers in Week 1 controlled the Raiders' zone-running game. Darren McFadden has mostly been bottled up, with his longest run from scrimmage covering eight yards.

Knapp said the Raiders moved the ball fairly consistently during the preseason and that the zone running game has worked well at his previous stops – including the Texans last year and his first stint in Oakland, when Justin Fargas rushed for 1,009 yards in 2007.

"I'm talking to my friends who call me and let me know, 'Hang in there, bud. You'll be fine. I know they're coming down on the run game,' " Knapp said. "It's like we tell the players. We want success right away, but we also have to understand that it takes a little time to develop."

Before starting against Miami, center Stefen Wisniewski had played just six preseason snaps in the new system because of injuries. Starting right tackle Khalif Barnes suffered a groin injury against Miami and has not practiced this week.

With relative youth along the line, Knapp said, the learning curve for the new blocking scheme might be longer than with his previous teams. Before the season, Knapp compared installing the new offense to operating a start-up company.

"It's making progress," Knapp said. "It's making progress. It may not look up statistically, but in the execution on cut blocks, combination blocks, we're seeing progress being made."

Injury report – Linebacker Rolando McClain (concussion) returned to practice in a limited capacity but is still going through the process of being medically cleared, coach Dennis Allen said.

Cornerback Coye Francies (concussion) was also limited. Barnes and cornerback Shawntae Spencer (foot) did not practice. Spencer, who recently had an MRI, said the diagnosis remains a sprained foot and he is unsure when he'll return.

Game on TV – Sunday's home game against Pittsburgh is nearly sold out and will be televised locally, a Raiders spokesman said.

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