Kovacs and Jamie Clarke have left Sincil Bank after having their contracts cancelled, while Richard Butcher, Aaron Brown and Sam Clucas remain on the transfer list.
Linganzi, meanwhile, moved to Deepdale on the recommendation of former Blackburn boss Sam Allardyce after a discussion with current Preston manager Phil Brown.
The Giants were down to 12 men when Wigan old boy Kevin Brown was sin-binned for tugging back Sam Tomkins, who remained in support after setting Richards away.