One candidate, according to Bob McGinn of the Milwaukee Journal Sentinel, is Packers running backs coach Alex Van Pelt.
"A source said the Bills were interested in hiring Van Pelt as quarterbacks coach but, with a year remaining on his contract in Green Bay, it's unlikely McCarthy would let him go," wrote McGinn on Tuesday.
Van Pelt, 43, has an extensive history in Buffalo, having spent nine seasons (1995-2003) with the Bills, starting 11 games at quarterback. After a brief stint doing color commentary for the Bills' radio network, Van Pelt became a coach with the team in 2006 and was eventually promoted to offensive coordinator shortly before the 2009 season.
The Bills had the 25th-ranked offense in 2009 and Van Pelt -- along with the rest of the Bills' coaching staff -- was fired after that season. Van Pelt joined the Tampa Bay Buccaneers' staff the next season, coaching quarterback Josh Freeman for two seasons before head coach Raheem Morris was fired.
Offensive coordinator Nate Hackett coached the Bills' quarterbacks this season. It's possible that coach Doug Marrone decided that Hackett, who at 34 is among the NFL's youngest offensive coordinators, would be better suited having a separate coach for his quarterbacks.
Most NFL teams have a quarterbacks coach separate from their offensive coordinator, although there are exceptions, such as Josh McDaniels filling both roles for the New England Patriots.