Sigthorsson faces spell on the sidelines due to ankle injury

The Iceland international could be unavailable for a period of time after picking up a knock in Sunday\'s league game. Ajax will have to make do without the services of striker Kolbeinn Sigthorsson after the Iceland international picked up an ankle injury in his side\'s 1-0 Eredivisie loss away against Groningen on Sunday.The former AZ attacker was part of head coach Frank de Boer\'s starting XI, but was forced to leave the pitch after only 19 minutes of play due to the knock.It is not yet exactly known how long Sigthorsson will be out of action due to the ankle problem. Ajax have revealed on their official website that the striker will undergo further examination on Monday to clarify the extent of the knock.Meanwhile, Eredivisie Live reports that the 21-year-old has withdrawn from the Iceland squad for the upcoming Euro 2012 qualifier away against Portugal on October 7.Ajax have dropped to fourth spot in the Eredivisie table following Sunday\'s loss. They have accumulated 15 points from eight games.