Chris Kirkland was a late absentee from the Wednesday line-up against Birmingham on Saturday.
The keeper was due to return to the starting eleven after recent injury and was warming up on the pitch before the Blues clash when he felt a twinge. That meant a last-minute team change, with Damian Martinez drafted in from his planned place back on the bench.
Gray said Glenn Loovens was taken off for the final 15 minutes of the Birmingham game as he had felt his hamstring tightening while Jacques Maghoma will be out for several weeks after suffering medial ligament damage.