Rory Best's participation in Ireland's World Cup quarter-final against Wales on Saturday is in serious doubt. Best sprained the AC join in his right shoulder during yesterday's 36-6 victory over Italy at Otago Stadium and is receiving treatment. A replacement for the Ulster hooker, who has been playing the best rugby of his Ireland career, has yet to be summoned and a clearer picture over his condition will emerge tomorrow. "Rory's doubtful for the weekend but we haven't written him off just yet," said manager Paul McNaughton. "We'll assess it tomorrow and have more information then. He's definitely doubtful. "He's getting manipulation at the moment. We'll have a better idea tomorrow after a morning's treatment." Ireland have already lost one hooker during the World Cup after