Keith Fahey has been ruled out for the remainder of the season after suffering a recurrence of a hip problem.
The 30-year-old Republic of Ireland international, who recently returned to his club Birmingham City from compassionate leave, requires further medical investigation and treatment to an injury to his hip and groin.
It makes Fahey's participation in Ireland's post-league season matches with England, Georgia and the World Cup qualifier Faroe Islands unlikely.
Blues boss Lee Clarke said it was "an absolute nightmare".
He told bcfc.com: "We got really concerned as he had a lot of bleeding in his groin area which came out in a bruise.
"When we had it scanned, the hip area was the problem so he is certainly out for the six games.
"Keith Fahey has shown in the last two away games what an outstanding midfield player he is. It was no coincidence that we put in two tremendous appearances away from home.
"We weren't conceding and we were playing good football with him in the team."