PARIS, Nov 6 (REUTERS) - Australian Pat Rafter announced on Friday he would not take part in the ATP Tour world championship in Hanover later this month because of a knee injury.

The Australian is currently ranked third in the ATP Tour rankings and had a chance to end the season as number one had he gone to Hanover.

"I just saw the doctor here in Paris. My left knee is a problem that I have been aware of for a while, and it's something that comes and goes.

"The doctor suggested rehabilitation for the next few weeks," said Rafter, who was beaten in the third round of the Paris Open on Thursday by American Todd Martin.

"Obviously I'm disappointed about having to pull out of Hanover. This would have been my biggest opportunity (to finish the year in top spot)," he said.

The U.S. Open champion, who was treated by tournament doctor Bernard Montalvan, said he would now be going to London then to his home in Bermuda for a rest before returning to Australia.

His withdrawal, following that of Dutchman Richard Krajicek, also because of a knee problem, clears the way for Briton Tim Henman to make it to Hanover, with fellow Briton Greg Rusedski, Slovak Karol Kucera and Russian Yevgeny Kafelnikov also in contention for one of the last two places.