It looks like the same type of groin injury which kept the big man out of action for four months, before the winter break.
But if the injury does not look as serious as first expected, the Swedish defender will still likely be out of action for a few games at least.
Martin O'Neil was wary about the situation during the post-match press conference today, but claims it has nothing at all to do with the first injury. He said he taking ''no risks'', that was the reason Mjallby was taken off.
In other news, Leeds United have pulled out of their £375,000 swoop for Irishman Colin Healy.
A spokesman for Leeds United said that they had watched the player but decided to reject their request.
It is a possibility that Leeds will move in for Healy at the end of the season, where they will be able to purchase the player on a free transfer.