Kilmarnock's Alistair Johnston faces an extended absence due to injury, with the club's defensive options severely impacted. The Canadian international was substituted off at half-time in Celtic's 5-1 win at Kilmarnock, with the Hoops 3-0 up at the break. Assistant manager Shaun Maloney described it as a precautionary measure. However, one former Premiership player has claimed the extent of Johnston's injury could be worse. Andy Halliday, speaking on Open Goal, claims that he has heard Johnston's injury is a bad one and that it may be worse than the reported six weeks. For now, we know that Johnston will miss the LASK ties and potentially the bulk of the September schedule. Johnston missed the majority of last season with a hamstring injury which required surgery. O'Neill has moved to rule out a recurrence of that injury, saying it's an issue lower down his leg this time around. The 28-year-old's absence will be felt and his return will be met with a resounding welcome by the support. Kilmarnock currently sit 11th in the Premiership, 42 points behind leaders Heart of Midlothian, with 37 goals scored and 65 conceded this season.