Rafael Nadal said on Friday he "hopes" to be ready for his opening match at the ATP Finals but admitted he has not been training at 100 per cent after an injury scare.
The 16-time Grand Slam champion pulled out of the Paris Masters last week with a knee problem, sparking fears that he would miss the season-ending finale in London.
When asked whether his knee would be ready for his first match against Belgium's David Goffin on Monday, the Spaniard told a pre-tournament press conference "I'll try my best," but admitted he had been wary during practice in recent days.
"I hope. And if I didn't believe I can be ready, for me, I wouldn't be here," said the world number one. "I'm working every day, practising well and just trying to be ready for the action."
He said it was impossible to predict whether his knee would be close to its best by the time of next week's final, adding that he was taking things day by day.
"You cannot predict what's going to happen," he said. "You work every day without thinking too much about what's going to happen."
Nadal insisted he had made no schedule demands on the organisers to gain additional time to recuperate from his injury.
If the Spaniard pulls out of the event it would be a huge blow to organisers, with the likes of Novak Djokovic and Andy Murray already missing from this year's event, giving the eight-man field a lopsided look.
- Stellar season -
Nadal , 31, has had a season to remember after an injury-ravaged 2016, winning the French Open and US Open and climbing back to the top of the world rankings.
Long-time rival Roger Federer, who scooped up the other two Grand Slams this year -- the Australian Open and Wimbledon -- said Nadal's absence would be a big loss.
"He's the number one player in the world, he's had the best season of us all and he's a superstar of our game so naturally it would be a big blow," said the Swiss.
"If he's here, to me that means it's already a very good sign," Federer, 36, added. "We hope he plays and hope he plays well,"
Nadal, who has never won the ATP Finals, said it was satisfying to be back in London for the year-end event after he missed out last year, admitting the absence of the trophy in his career played on his mind.
The Spaniard faces Goffin on Monday evening in the last of the first batch of matches. Two groups of four players play in a round-robin format before semi-finals and a final.
The other players in Nadal's group are Dominic Thiem and Grigor Dimitrov, while Federer competes against Jack Sock, Marin Cilic and Alexander Zverev, who has climbed to number three in the world in a breakthrough year.
Nadal is guaranteed to end the year as world number one, irrespective of his performance at the finals, which begin on Sunday and end on November 19.
Fitness permitting, all eyes are on a potential final between Nadal and Federer, with the Spaniard keen to atone for four defeats out four to his Swiss rival this year.
"It would be great to finish the year playing against him again," said Nadal.