But he does know how potent a backfield would be with him and fellow running back Frank Gore in it.
"I think it would keep defenses off balance," Westbrook said. "We'll see how it goes."
How it goes is anyone's guess. Westbrook, who was signed on Aug. 16, said he's recovered from a hamstring injury and is familiar enough with the playbook to play as much as needed. How much?
"That's something you'll have to ask coach Jimmy (Raye)," he said. "He would know much better than I would. I'm preparing to play, but I don't know what my role will be."
Jimmy Raye, the 49ers offensive coordinator, said he intends to make use of Westbrook – and perhaps even in tandem with Gore – but he's uncertain if Westbrook will play a lot.
"I think you'll see some of him," Raye said. "To what extent, I don't know. As I said when … we first acquired him, my biggest concern with a player that doesn't go through the offseason program and training camp, you run the risk of a setback from a strain or pull, and that's what happened to him.
"I think he's going to be OK, but we don't have a set number of plays for him because you couldn't very well do that and take practice time away from the other things you're going to do, not knowing how much availability you're going to have with him."
At the very least, having Westbrook around may be good thing for Gore, who said they each want to out-do each other on the field.
"It's going to be like friendly competing," Gore said. "If he does something big, I'm going to try to do something big."
Westbrook said he ready to do something big now. All he needs is a green light.
"I think I'm ready to play," he said. "Jimmy's the coach, so it's his decision as far as who plays and how much. Whatever he says goes, but I'm ready."
Gore knows that Westbrook's primary role will be to make sure Gore isn't worn down during the course of the season. So having a new teammate is a nice addition.
"I love it," Gore said.
Does that mean Gore will take a few more breaks during games?
"I'm not saying I love it like that," he answered.
INJURY REPORT: Linebacker Ahmad Brooks (lacerated kidney), center Eric Heitmann (broken leg) and wide receiver Kyle Williams (sprained toe) are definitely out for Sunday's game. Cornerback Will James (ankle sprain) did not practice Thursday and is day to day. Linebacker Diyral Briggs (concussion) returned to practice, although it's uncertain if he'll play.