The club has cancelled David Gonzalez's contract. The 29-year-old Colombian goalkeeper, who signed for City in 2009, has been on loan at Aberdeen for the past six months.
Loris Karius, the Germany Under-16 goalkeeper signed from Stuttgart in 2009, has joined Mainz, where he was on a season-long loan, in a permanent deal.
The club would like to wish both players the very best for the future.