Left 4 Dead Prequel In Development?

Zombie co-op series Left 4 Dead may be returning soon. Rumor has it that a third installment is in development and it'll be a prequel.

CVG reports that Overkill Entertainment is working on the L4D prequel. Overkill is the studio responsible for the PSN/PC shooter PAYDAY: The Heist. The company announced in May that they were working on a project with Valve.

At the time, Overkill and Valve's collaboration sounded more like a crossover game. The former described the game as a "very cool blend of Payday and Left 4 Dead." An L4D prequel doesn't fit that description exactly. What about that premise says Payday?

A prequel to L4D might take place before or during the initial zombie outbreak. If so, I suppose it's possible to incorporate the criminal crew from Payday somehow. Maybe they try to steal research from a secret lab and accidentally unleash the virus that turns everyone into zombies?

Regardless of what approach they take with the prequel, Overkill seems like a good development partner for Valve. Payday is pretty similiar in design to L4D. It has four-player co-op, ammo and health sharing, dynamic enemy spawns, and so forth. Making the jump to L4D shouldn't be that hard for them.