Kim Clijsters could surrender her number one ranking to fellow Belgian Justine Henin-Hardenne this week but she still considers Serena Williams to be the world's top player.

"She gets that extra and that makes her I think still the best player in the world, no problem," said Clijsters on Monday before the start of her defence of the Porsche Grand Prix title.

"If she was injury-free she's the toughest to beat out there. If Serena played the number of tournaments that I play I definitely think that she would be number one.

"But tennis is in part consistency and being fit and trying to stay fit, and definitely this year until now I've been very consistent, more than she has."

Serena is currently ranked three behind Clijsters and Henin but the American has missed a number of events this season due to a knee problem that required surgery at the start of August.

Clijsters and Henin have clashed repeatedly on and off court, with Henin twice beating the world number one in Grand Slam finals at the French Open and the U.S. Open.

Clijsters' father even questioned Henin's dramatic physical improvement but Henin said on Monday that she could only get stronger.

"After the training I did last December I said that everything was possible," she said. "But I think maybe I will not reach 100 percent of my physical possibility until the end of next year."

OPTIMISTIC DAVENPORT

Clijsters, who is likely to start against the opponent she defeated in the 2002 final, Slovakia's Daniela Hantuchova, maintains she is still on good terms with Henin.

"We've laughed at it. We're colleagues and friends, a combination, and it doesn't matter if we're playing (against each other). We play to win, but then we get back in the locker room after the match and we're talking.

"That's what it should be all about. We're rivals on the court, but you can be friends too."

American Lindsay Davenport, the number three seed, is now hoping to get through the remainder of the season before undergoing surgery on a swollen nerve in her left foot.

It has been bothering her for several months and she hinted during the U.S. Open that surgery was imminent.

But she said on Monday: "I'm going to go until I feel I can't go any further, because at this stage of my career it's hard to sit out months and months at a time.

"I would like to try and play once or twice more this year. It's hard to keep having time off, and I think indoors is my best surface and matches are typically a little bit shorter, so I'm optimistic."