The front man limped out of the Republic of Ireland’s 0-0 draw with Northern Ireland during the international break.
Alex Neil addressed the issue at his press conference on Thursday morning ahead of the game against Blackburn on Saturday.
“I don’t think we’ll see Sean until January which is disappointing,” he said.
"Him coming back although he didn't feature in every match really boosted competition for places and his return coincided with seven games unbeaten for us.
“We just felt like we were getting him going, I thought he put in a really good performance at Bristol City.
"We'd gradually built up his minutes but then the week where he would have a down week with us and recovered, he then has to go away on international duty.
"We're just really frustrated and disappointed."
There is better news however on Alan Browne who is fit despite pulling out of Ireland duty due to a persistent shoulder problem.