Where might Pats look for coordinator?

With the news Thursday night that Patriots offensive coordinator Bill O'Brien has agreed to become the next head coach at Penn State, as reported by ESPN's Chris Mortensen, who might Bill Belichick tap to fill the vacancy?

O'Brien will be with the Patriots throughout the NFL playoffs (a fact confirmed by ESPN's Adam Schefter). So this question is more about the 2012 season and beyond.

A Josh McDaniels return, if he's ultimately available (he was not fired when Rams coach Steve Spagnuolo was shown the door and is still under contract in St. Louis), makes a lot of sense. It was McDaniels' departure following the 2008 season to become Broncos head coach that opened the door for O'Brien's ascent up the Patriots' coaching ladder, giving him the chance to work with Tom Brady as quarterbacks coach/playcaller. Unlike some other Patriots assistants who have left to become head coaches elsewhere, no bridges have been burned when it comes to McDaniels and the Patriots.

This would fall in line with Belichick's past hires, in which he placed a premium on their having a background in the team's system. Belichick isn't about to change the offensive system, which has been expanded over 12 years -- from Charlie Weis, to Josh McDaniels, to Bill O'Brien -- so the new coordinator is going to have to adapt to what is already in place.

The transition would naturally be easy for McDaniels -- again, if he was ultimately available and interested in a return.

If Belichick looks in-house, coaches such as Brian Ferentz (tight ends, four NFL coaching seasons) and Chad O'Shea (receivers, nine NFL coaching seasons) could draw consideration in a setup similar to what McDaniels and O'Brien initially had -- play-calling duties without the title of coordinator. Belichick already has two respected veteran assistants in Dante Scarnecchia (offensive line) and Ivan Fears (running backs), which also would factor into his decision-making process.

Just like with players on the roster, Belichick has a solid track record of grooming coaches within the offensive or defensive systems, giving them more responsibility as it is earned.