DO NOT PUBLISH - Tennis: Isner, America's No. 1, may withdraw from Australian Open

SYDNEY (Bloomberg) - John Isner, the highest-ranked American tennis player, may pull out of next week's Australian Open because of a knee injury.

Isner, ranked 13th on the ATP World Tour, lost his opening match 4-6, 4-6 at the Sydney International to compatriot Ryan Harrison on Wednesday.

Afterwards, he told reporters he'd been struggling with a bone bruise on his knee.

"I got a decision to make shortly," the 27-year-old said. "It was a lot better than it was six days ago, but it wasn't 100 per cent. What I have needs time, that's all it is."

The Australian Open, the season's first Grand Slam, starts on Monday in Melbourne. Isner's best result there is a fourth-round spot in 2010.

Andre Agassi's victory in 2003 is the last one in Australia for an American man, and no US male player has won a Grand Slam singles title since Andy Roddick took the US Open in the same year. Roddick retired last year.

Rafael Nadal of Spain withdrew from the Australian Open last month, saying a stomach virus would not give him sufficient time to get ready to compete.