The Northern Ireland international midfielder, who has been the most consistent performer for Blues so far this season, is to undergo scans on the injury which will determine how long he is likely to be sidelined for. "In the last couple of months he has been our best player by a million miles. He has set the standard."
"When we get the results back we will know how serious it is, but it doesn't look too good at the minute," Blues boss Steve Bruce has said.