Derek McInnes who only brought the Scotland Under-21 striker in on-loan from Stade de Reims on the final day of the transfer window.
An Aberdeen statement confirmed: "Upon further investigation a scan has shown Fraser has suffered a significant tear on his thigh that will keep him out for a period of time." Hornby, who has made just five appearances for the Dons, suffered the injury when he hit a first half shot in Saturday’s win over Kilmarnock.
There are only three games left before the split and then five games after that and it all depends on how Hornby responds to treatment, if he will be able to play a part in the final few games.
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