City make a Killen on striker
The 21-year-old signed for The Latics for £200,000 in July last year but the deal included a clause that made a further £25,000 payable once the player had made 30 appearances.
Killen has started 13 games and come off the bench 13 times, meaning another four games played will make the fee payable.
The New Zealand international has scored four goals during his stint at the club and the Boundary Park side will now have to hand the further cash over to City.
Oldham also had to pay Chesham United an extra £10,000 for Fitz Hall after he made 20 first team appearances.
Meanwhile, Canadian striker Carlo Corazzin has finally gone under the knife for an operation on his knee injury, while young winger Adam Griffin has joined Nationwide Conference side Chester City on work experience.