The Buffalo Bills have signed quarterback duo Matt Leinart and Thaddeus Lewis following an injury to Kevin Kolb.

Kolb was forced off during his side's pre-season loss to the Washington Redskins on Saturday with what the Bills fear could be a career-threatening head injury.

His injury left the Bills short in the quarterback department, with rookie EJ Manuel also sidelined for at least the rest of pre-season having undergone surgery on a knee injury.

Leinart, a former first-round draft pick, joins his fourth different NFL franchise having been a free agent since leaving the Oakland Raiders during the off-season.

Lewis, meanwhile, joins the Bills from the Detroit Lions in a trade that sees linebacker Chris White go the other way.