Nikolay Davydenko admits he will not have enough time to prepare for his semi-final clash against Roger Federer at the Barclays ATP World Tour Finals on Saturday afternoon.

The Russian will take to the court at London's O2 Arena only 15 and a half hours after finishing his final round-robin match, where a 7-6 (7/4) 4-6 6-3 victory over Robin Soderling booked his semi-final spot.

The world number one, in contrast, has not played since losing to Juan Martin del Potro on Thursday night.

Davydenko, who is also struggling with a leg injury and breathing problems, said: "I have no time. Today I play night session and tomorrow at 2pm. It's not my mistake. I hope I'll be fit for tomorrow."

To add to the 28-year-old's worries, he goes into the match having lost all his previous 12 meetings with Federer.

Davydenko, though, is hopeful he will at last be able to better the world number one and reach a second consecutive final.

He said: "Every 12 times I was coming and believing I can win. But I know Federer is older, I'm also older. Maybe I start to play better and Federer not so good? We'll see."

After Thursday night's confusion, Group B also ended up being tight, with Soderling, Davydenko and defending champion Novak Djokovic - a 7-6 (7/5) 6-3 winner over Rafael Nadal yesterday - all ending up winning two matches and losing one.

To the relief of the tournament organisers, though, there was a clear difference in sets ratio this time, with Soderling winning the group courtesy of the set he took against Davydenko and Djokovic the unlucky man.

The Swede has almost 24 hours to recover before he returns to the O2 for his semi-final against Argentinian Del Potro, and he said of the match: "It's going to be tough. He plays really well. He serves big. He's hitting his forehand very well and plays fast.

"He doesn't give you many chances. He's probably very confident now, beating Roger. So I have to step it up at least one level. But I think I can do it. I played good this whole week."

Djokovic had battled hard to put himself in contention despite the strain of a year in which he has played nearly 100 matches clearly catching up with him.

He said after beating Nadal: "Unfortunately for me, the exhaustion came in the tournament where I should have been the freshest. But, still, I managed to get two out of three wins.

"If I finish today the season, I will be very happy to finish in this way, and just hope to rest well for 2010."

Nadal, meanwhile, is determined to end the year on a winning note at the Davis Cup final next weekend, when Spain take on the Czech Republic in Barcelona.

The Majorcan, who did not win a set in three matches in London, said: "I am confident. I know it's going to be a difficult final. The change (to playing) on clay is going to be a big change. It's going to be difficult in the beginning.

"But that's a big motivation for me, to finish the year winning. And I have the opportunity there to play well, to play good tennis on clay, and to win, to win something important for my country and for my friends."