According to ProFootballTalk's rumor mill, San Francisco 49ers head coach Mike Nolan may already be fed up with defensive coordinator Billy Davis and his less than stellar defense.

From ProFootballTalk:
In the wake of a 41-0 trouncing by the Kansas City Chiefs, talk is intensifying in league circles that Niners defensive coordinator Billy Davis will be fired at the end of the season, if not sooner.

Davis was hired by Mike Nolan in February 2005, after Nolan was named the 49ers' new head coach.

We've previously reported that players have been getting mixed signals from Davis and Nolan (a former defensive coordinator) regarding the team's attack, which at times has been a 3-4 and at times has been a 4-3.

If Davis is dumped during the season, Mike Singletary (the team's assistant head coach/defense) possibly would team with Nolan to handle the coordinator duties. It would be a good learning experience for Singletary, who widely is regarded as a guy who'll be a head coach in the NFL before too long.