[WORLD CUP 2010 COUNTDOWN] Following knee surgery Wednesday in Los Angeles to repair a ruptured patellar tendon in his left knee, American defender Oguchi Onyewu's rehabilitation process could be as long as six months -- a period that could jeopardize his chances of representing the USA at the 2010 World Cup.

Onyewu, who landed awkwardly on his knee late in the USA's qualifier against Costa Rica on Oct. 14, was initially projected to face a his recovery period of three-four months. The new estimate came after national team physician Dr. Bert Mandelbaum operated on Onyewu.

A six-month layoff would mean Onyewu could be ready to return to action for AC Milan in mid-April -- just a month before the Serie A season  ends May 9.

The loss of Onyewu, the USA's most indispensable defender, would be severe blow. His absence from the home qualifier against El Salvador in September -- the only Hexagonal game he missed -- was certainly felt.

Onyewu's injury came a day after forward Charlie Davies' chances of playing in the World Cup were almost certainly wiped out when he sustained serious injuries in a car crash.

As it is, Jay DeMerit, Onyewu's partner in the middle of the U.S. defense during its strong Confederations Cup run, just had a cornea replacement operation and is also sidelined.