AC Milan defender Oguchi Onyewu will undergo tests in the coming days to determine the extent of his knee injury.

Onyewu hurt his left knee playing for the United States during Wednesday night's World Cup qualifier against Costa Rica.

A statement from AC Milan read: "The US football federation have informed us of Oguchi Onyewu's suspected tendon rupture of his left knee.

"The player, who is in the United States, will undergo further tests and if the diagnosis is confirmed, he will have surgery.

"Milan doctor Massimo Manara is in constant contact with Onyewu."

If a rupture is confirmed, the 27-year-old will be out of action for at least three months.

Onyewu signed a three-year contract with AC Milan this summer.