ALAMEDA — Michael Crabtree wanted to be a Raider and was all smiles a day after signing his four-year, $35 million extension.

“It’s always nice to get it done,” Crabtree said Thursday. “That way we can just go play football. You ain’t worried about where you’re going to be next year. It’s pretty neat that you know you’re wanted and you want to be on a team, and you’re here.”

Crabtree, 28, who was playing on a one-year, $3.2 million deal this season, had in recent weeks brushed off any talk about his future. But both sides saw value in getting Crabtree locked up before he hit free agency, and that allowed the deal to come together.

“People upstairs handled it good with my agent and took care of things and got it done,” Crabtree said.

Crabtree is encouraged by the Raiders’ direction and has developed tremendous relationships with quarterback Derek Carr and his fellow receivers.

“We building,” Crabtree said. “We got some good guys in the locker room, offense and defensive-wise. (Carr) has been good. Amari’s been good. Seth (Roberts). We’ve got a good core, a good receiving corps right now. I feel like we’re going to build on that. We’re just growing and I’m just happy to be here and really take on whatever role they need me to take on.”

Part of that role with the Raiders has been as a leader in the locker room, an area in which he didn’t possess the best reputation during his six years with the 49ers.

“You always hear a little bit about people before they come,” veteran safety Charles Woodson said. “Over the years, there’s been some talk and rumblings about him not being a good teammate and things like that.

“You try not to prejudge people. I know how it was when I left here and went to Green Bay. I was prejudged by a lot of people. You try not to get into that, and I didn’t see any of that from him and I still don’t. He’s a great teammate from what I know and what I see and what I’ve been around. I think everybody in here would say the same thing.”

Crabtree’s signing further solidifies an offensive core that stands to be locked up for several years, led by players such as Carr, running back Latavius Murray, wide receiver Amari Cooper, tight end Clive Walford, center Rodney Hudson and left guard Gabe Jackson. Fullback Jamize Olawale was given a three-year extension on Tuesday as well.

Up next: Donald Penn? The team’s starting left tackle will be a free agent in the offseason. Penn, 32 and in his 10th NFL season, is optimistic about re-signing with the Raiders, but isn’t giving it much thought right now.

“The best thing to do is let it play out,” Penn said. “Let everything work out for itself. If I play good on Sunday, it’s going to be better. That’s all I can worry about and focus on, finishing the season strong. That’s my main focus right now, and hoping we can sneak into the playoffs. After the offseason and my agent takes care of all that, all that stuff will happen.”

Regardless of his own situation, Penn is happy to see the Raiders making moves to keep their key offensive pieces together.

“That’s great,” Penn said. “One thing about us, with all the stuff that’s going on, we’re still sticking together, we’re still upbeat. We’re still all having fun. We’re still coming to work together. That’s good. That’s why I am glad they are keeping the core guys, because we get along together, we love each other and we play for each other.”

Crabtree is on pace for his second 1,000-yard season of his career, but it’s Cooper who could get there this weekend. The rookie is just 80 yards away from becoming the first Raiders receiver to reach the 1,000-yard mark since Randy Moss in 2005. “I think it will be a cool accomplishment,” Cooper said. “It means a lot to accomplish something that hasn’t been accomplished in a long time.” If both Cooper and Crabtree, who is at 760 yards with four games to play, reach the mark, they’ll become the first Raiders teammates to do so since Hall of Famers Jerry Rice and Tim Brown both accomplished the feat in 2001. Crabtree has enjoyed mentoring and watching Cooper during his rookie year and said he’s been pushed by him. “Since the day he stepped foot on the field, dude’s been working hard,” Crabtree said of Cooper. “Anything to get better. I just let Coop be Coop. He got it. He got the motivation and he got the ambition to be great. I’m just watching too at the same time. We’re making each other better. That’s a good thing.”

Cooper shows up on Thursday’s injury report with a foot injury that limited him in practice. It’s likely not a serious injury that would keep him off the field Sunday in Denver.

Khalil Mack returned to practice as a full participant after missing Wednesday’s with a minor knee ailment. He said he’s good to go for Sunday’s game.

Center Rodney Hudson was also back for the first time in a week and took first-team repetitions. He’s missed three of the past four games with a sprained right ankle. He returned to practice on Dec. 10 but had a setback and missed his second straight game. As long as he makes it through Friday’s practice in good shape, he looks on track to return Sunday.

Running back Taiwan Jones, who missed the past two games with a knee injury, also returned to practice for the first time since getting hurt Nov. 22 at Detroit. He was limited.