Rafael Nadal says he is determined to improve his poor record on indoor courts as he bids to win the ATP Finals for the first time in his illustrious career.

Just one of the Spaniard's 86 singles titles has come on an indoor hard court, back in Madrid in 2005.

Nadal has earned a berth at the end-of-season ATP Finals every year since that year but has been forced to withdraw on six occasions. 

Speaking Friday ahead of this year's tournament at London's O2 Arena, he said there were a number of factors for his failure to shine indoors, including fatigue at end-of-season events and a preference for other surfaces.

"We can find excuses or reasons but at the end of the day the numbers are the numbers," Nadal said. 

"I think I have played less indoors than in other places without a doubt."

The second seed, who drew level with Roger Federer on 20 Grand Slams by winning last month's French Open final, said his game was not ideally suited to fast courts.

"The indoor surfaces have been not ideal surfaces for my tennis game since the beginning of my career," said the 34-year-old.

"I think I am able to play a little bit better the last couple of years indoors than what I did at the beginning of my tennis career without a doubt but that's the numbers and I can't say something different. I hope to change that this week."

Last week Nadal reached the semi-finals at the Paris Masters, where he was beaten by Alexander Zverev.

He said his four matches indoors in Paris had sharpened up his game but he did not know how close he was to "perfect preparation" for the London tournament, which starts on Sunday.

50th anniversary 

The 50th anniversary of the first staging of ATP Finals, which features the best eight players of the 2020 season, has been marked with the naming of two round-robin groups, Tokyo 1970 and London 2020.

Nadal will compete in Group London against defending champion Stefanos Tsitsipas, US Open champion Dominic Thiem and Andrey Rublev. 

World number one Novak Djokovic will face Daniil Medvedev, Zverev and Diego Schwartzman in Group Tokyo.

Nadal said the absence of crowds due to the coronavirus pandemic meant conditions would be radically different this year as London prepares to play host for the final time.

"Sad playing with no crowd in this amazing stadium," he said. "It is something that is not perfect but we can play tennis so we can't complain at all. We are very lucky."

The Spaniard said the experience of playing the finals in the British capital had been "one of the best" but backed the decision to move the tournament to Turin from next year.

"I think tennis needs to keep moving," he said. "At the same time it's not fair to finish the world tour finals here without crowds, with this situation but that's the thing that is happening today in this world."