Aaron Morris' knee injury is worse than first anticipated after further scans revealed the Aldershot man has suffered cruciate ligament damage.
The Shots midfielder had initially been diagnosed with a dislocated kneecap having been stretchered off after his knee gave way during Easter Monday's 3-2 victory over Oxford.
But after the Welshman returned to Cardiff to receive treatment and undergo a further MRI scan, it was confirmed he had sustained ligament damage and will now face an even longer spell on the sidelines.
Manager Andy Scott said: "It is a devastating blow for Aaron who has performed well since I arrived at the club. We send him our best wishes and hope for a quick recovery."