Actor's reason is unknown, but studio is looking for a new costar for Sandra Bullock

Pop Quiz: You’re Keanu Reeves, about to receive $11 million for Speed 2. Why do you back out? That was the question of the week when news broke that Reeves would not return to film next summer’s surefire blockbuster. Initial speculation that he had dropped out to tour with his band, Dogstar, was dismissed as implausible. More likely is that Reeves — who recently broke his ankle in a motorcycle accident, and who just finished a grueling shoot for the upcoming action flick Chain Reaction — is simply hurting. Says Reeves’ manager, Erwin Stoff, ”He didn’t want to do two action movies back-to-back.”

But more than Reeves’ body may have been bruised. Costar Sandra Bullock’s matching $11 million payday meant Reeves would share the driver’s seat in terms of the size of their roles. Stoff denies that was a consideration. For her part, Bullock said she would proceed with the sequel for now, ”pending her approval of the male lead.”

Who might that be? Hollywood hunks are surely scrambling to take Reeves’ place. Meanwhile, one observer doesn’t foresee a problem changing leads. Says screenwriter Larry Ferguson (The Hunt for Red October): ”Remember Alec Baldwin? I don’t know how he changed into Harrison Ford in Patriot Games, but he did, and nobody said anything.”