By his count, Raiders starting middle linebacker Rolando McClain had suffered zero concussions in his football career until Sunday at Miami.

Even then, he didn’t truly realize he had a concussion until after the game, when doctors examined him and made the diagnosis.

“You take hard hits all the time,” said McClain, who missed practice Wednesday because of the concussion and an ankle injury. “It’s football. I’ve been playing for a while and you always take hard hits. Obviously, the doctors saw something. It was more in the game where I felt like, ‘Well, dang, I don’t feel like myself.’ It’s one of the more scary injuries. With an ankle, you know what’s wrong. But when it’s your head, you don’t know.

“I guess that’s why it’s so important nowadays to try to limit some of those things, take all the precautions that we are taking now with the significance of these head injuries. So I’m just doing whatever the trainers tell me to do and hopefully I can get back pretty fast.”

McClain will have to pass a series of tests before he is cleared to return to practice and play against Pittsburgh.

“Obviously you don’t want to rush anything with the head, but it is what it is,” he said. “I’m just doing whatever it is I can do to get back. We’ll see.”

Raiders coach Dennis Allen said team doctors and trainers on Sunday didn’t think it was a “major” concussion.

“Seemed like a minor deal," Allen said. "It’s kind of a precautionary deal that we’re going through the whole process to make sure he’s fine."

Cornerback quandary: Starting right cornerback Shawntae Spencer was still on crutches Wednesday and still had a walking boot on his sprained right foot, which he injured in the fourth quarter against Miami. Barring a miraculous recovery, Spencer will miss Sunday’s game, and the Raiders have dealt with enough sprained feet to know that injury can sideline players for weeks if not months.

Pat Lee replaced injured left cornerback Ron Bartell (broken shoulder blade) in the starting lineup last week and wound up sharing time with Joselio Hanson. Hanson is listed second on the depth chart at right cornerback, behind Spencer, but free safety Michael Huff took some snaps at cornerback Wednesday, and Allen said Monday that moving Huff to corner is an option.

McFadden staying positive: Running back Darren McFadden said he’s shocked but not frustrated over his slow start -- just 54 rushing yards in two games.

“That’s a big shock to me,” McFadden said. “You know this is the National Football League, so everyone is going to have bad games. So you just have to go out there and keep pushing and just get better.”

McFadden said he refuses to let himself become frustrated.

“If you get frustrated, you only get down on yourself,” McFadden said. “So you have to just go out there, and keep grinding, keep pushing forward.”

The Raiders’ zone blocking scheme, installed by new offensive coordinator Greg Knapp, has yet to get untracked. But McFadden said he hasn’t lost faith.

“I just feel like going with the zone system is one of those situations where you’re going to have to keep hitting it until you get going,” McFadden said. “It’s going to be one yard here or two yards there, but eventually it’s going to start popping.”

Add one: Cornerback Brandian Ross went through his first practice as a Raider since being signed off of Green Bay’s practice squad. He said he’s trying to learn the Raiders’ defense as fast as he can in case they need him to play Sunday.

“That’s the plan,” Ross said. “Try to pick (it) up ASAP so I can help get this first ‘W’ here.”

Ross signed with Green Bay last year as an undrafted rookie from Youngstown State and was on the Packers’ practice squad in 2011 while new Raiders GM was a Packers personnel man.

“Actually, when another team wanted to sign me last year from the practice squad, he was the one I talked to and he convinced me to stay there,” Ross said. “It was best for my career at the time to stay there.”

Ross spent last year learning from veteran defensive backs such as Charles Woodson and facing Packers quarterback Aaron Rodgers and a star-studded stable of receivers, including Greg Jennings, Jordy Nelson, Donald Driver and Randall Cobb.

This time, Ross said, McKenzie had no trouble convincing him it was time to leave Green Bay and join the Raiders 53-man roster.

Extra points: Starting RT Khalif Barnes (groin) missed practice. Willie Smith will start at right tackle Sunday if Barnes can’t play. … CB Coye Francies (concussion) missed practice.

Follow Raiders reporter Eric Gilmore on Twitter: @CBSRaiders.