Rafael Nadal is hopeful of being fully fit for the ATP Finals in London.
The world number one was forced to pull out of the Paris Masters last weekend after suffering an abdominal injury and has been in a race against time to recover.
Speaking at the O2 Arena, he said: "I need to go day by day. I'm happy to be here because after last Saturday in Paris I didn't know if I would have the chance to be here.
"I need to see how things evolve every single day. I have good hopes to be 100% ready for Monday."
Nadal does not play his first match until Monday night, when he takes on defending champion Alexander Zverev.
The Spaniard had been unable to serve because of the injury but said: "I started yesterday, very slow.
"I have been serving very well in Bercy (Paris), I had good matches, so I am confident that I can be very competitive but of course it's a tournament that you will face the top guys since the beginning so you need to be 100% ready."
Indoor hard court has never been Nadal's favourite surface and injury has often got in the way of his participation at the ATP Finals.
The Spaniard has withdrawn ahead of the tournament six times since he first qualified in 2005 and two years ago was only able to complete one match.
He insisted he is not thinking about the Davis Cup finals, which begins on 18 November, but he will surely not want to miss the chance to compete in Madrid.
Another factor is the race to finish the year as world number one. Nadal overtook Novak Djokovic on Monday but needs either to reach the final with three group wins or lift the trophy to guarantee holding on to it.
The US Open champion said: "Of course I would love to be the year-end number one but I always said it was not my personal goal because I did not follow that (path).
"If I did I would be flying to China after New York because I was in a positive position. But that doesn't mean I am renouncing to try to be number one. Not at all. I am fighting for it."
Nadal is the veteran in the Andre Agassi group being at least 10 years older than Zverev, Daniil Medvedev and Stefanos Tsitsipas, with the latter two making their debuts.
Italian Matteo Berrettini is the other debutant and he finds himself with a formidable task in the Bjorn Borg group taking on first Djokovic and then Roger Federer and Dominic Thiem.
Djokovic has made no secret of how much he values records and tying Pete Sampras by finishing a year ranked on top of the world for a sixth time would be another notable one.
"Obviously that serves as a great motivation," he said. "The ranking situation is not only dependent on me but I'm going to try. I've historically played well in the indoor season."
The clash between Djokovic and Federer is likely to be the highlight of the group stage, and it will be a first meeting since their dramatic Wimbledon final in July.
"I'm very excited to play against Novak again here, happy to be in his group," said Federer. "Wimbledon was epic. That was a special match for both of us, maybe a bit more for him but that's OK, I moved on a long time ago."
Federer defended his decision to pull out of January's ATP Cup - where he had been due to face Andy Murray - for family reasons and revealed he will not play a tournament between here and the Australian Open, although he does have a number of exhibitions lined up.