SHANGHAI, China — Roger Federer doesn't like hearing himself announced as No. 2 in the world, and hopes his aching back doesn't hamper his pursuit of regaining the top spot.

"I just don't like the ring of it," the defending champion said Saturday with a smile on the eve of the season-ending Masters Cup. "It sounds a bit awkward to me. It is a challenge to get back to No. 1."

The round-robin tournament features the top eight players, and Federer will meet Gilles Simon of France on Monday. Andy Roddick will play Andy Murray of Britain.

Rafael Nadal, who will skip the event because of an aching knee, has wrapped up the year-end top ranking. So Federer is looking at Shanghai as a chance to build some momentum for 2009.

The Australian Open in January will be his first chance to tie Pete Sampras' record of 14 Grand Slam titles after winning the U.S. Open in September.

"I haven't been thinking about it much," Federer said. "Once I go on vacation, I'll have plenty of time for that."

The biggest question is his back. Federer, who withdrew from the Paris Masters last week, has been getting daily treatment and taking painkillers.

"It's way better than last Friday," Federer said at the news conference attended by the eight Masters Cup players, who dressed in matching gray suits and black silk shirts.

Still, he doesn't know quite what to expect when he faces Simon.

"I'm not sure because I haven't been pushing it to the very limit," said the Swiss star, who added he's worried he could tweak his back again. "It just needs as much time as possible."

Still, he declared himself the favorite, an opinion echoed by other players, though some of them have been in better form in recent weeks.

"I'm here to win," Federer said. "I'm not here just to participate."

Roddick, who has been recuperating from injury, also said he's feeling fit, though he's looking forward to the offseason to get back in peak form. Unlike some players, he doesn't use the break to rest up, saying he starts getting anxious during down time.

"I was just telling my fiancee, I don't know how I'll get through a honeymoon," Roddick said. "How am I going to sit still for five days?"

He also believes he has about four years of competitive tennis left.

"My bad days still are pretty good in the scheme of things," said Roddick, who's still looking for a fulltime coach after splitting with Jimmy Connors.

Jo-Wilfried Tsonga, one of four players making his Masters Cup debut, was the last man to clinch a spot in the elite field, winning in Paris.

"For me, it's just amazing. It's a dream," said Tsonga, who plays fourth-ranked Nikolay Davydenko on Sunday after No. 3 Novak Djokovic opens the event against Juan Martin del Potro. The Argentine earlier in the year won 23 straight matches and four consecutive tournaments.

Tsonga, who thinks the indoor Qi Zhong Tennis Center will suit his game, has improved in the ratings despite missing three months recuperating from knee surgery — a break that may have worked in his favor as other players wind down the long season.

"I feel great," Tsonga said, "stronger than at the start of the year" when he reached the Australian Open final, losing to Djokovic.

Djokovic, who dropped all three of his matches here last year and complained he was exhausted after playing a heavy schedule in his breakthrough season, said he's feeling better this time. But he's lost in the round of 16 in his last two tournaments.

"I haven't lately found my rhythm," he said. "Physically, I feel good."