Aston Villa have released five players, including former captain Richard Dunne.
Eric Lichaj, Andy Marshall, Jean Makoun and Simon Dawkins have also been told that they can leave the Premier League club.
Dunne, 33, joined the Villans in 2009 following a nine-year spell with Manchester City.
Celtic manager Neil Lennon recently admitted that he could be tempted to sign the centre-back on a free transfer.