Rafael Nadal expects to be fit for the Nitto ATP Finals in London where the season could end with another bout with perennial rival Roger Federer.
Spain's Nadal pulled out of the Paris Masters last week with a right knee injury, but is top seed here, with Federer second seed at the O2 Arena.
"If I didn't believe I could be ready for Monday I wouldn't be here," Nadal said at the pre-tournament media conference on Friday.
"I don't have to make a decision. I'm going to play. That's my feeling today.
"I had problems in Paris a week ago. I go day by day, how I'm feeling.
"I cannot predict what will happen, but my feeling now is I'm going to play and try my best."
Nadal faces David Goffin of Belgium on Monday evening in the last of the first round of matches. Two groups of four players play in a round-robin format before semi-finals and a final.
Nadal insisted he had made no schedule demands on the organisers which would give him additional time to recuperate from his injury.
"I didn't have any request. I didn't ask anything," he said.
Federer hopes the format, which sees each group play on a day-on, day-off schedule, will help Nadal to nurse his body through the event.
The 36-year-old Swiss said: "With the day rest, in between each match, that's big for him. To be able to have that day rest, let the knee heal itself a bit.
"We hope he plays and hope he plays well."
With last year's winner Andy Murray and runner-up Novak Djokovic absent through injury, there will be a new finals champion for the first time since 2011, when Federer won for a sixth time.
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.
He qualified for finals previously 12 times, withdrawing on five occasions, including 12 months ago.
And Nadal, who won the French and US Opens in 2017 to take his grand slam tally to 16, has never won the year-ending event.
Federer missed the 2016 event after ending his season prematurely b ut he responded phenomenally in 2017, winning the Australian Open and at Wimbledon to take his grand slam tally to 19.
Federer opted out of the clay court season and the French Open in 2017 after hurting his knee on the surface in 2016.
He is considering how to schedule his campaign in 2018 and has not ruled out a return to clay.
"For next year everything's back on the table, anything's possible," Federer added.
"There's no guarantee I'm going to play as well as I did this year at the beginning of next season. I have to take everything into consideration."
World number seven Stan Wawrinka is also absent due to injury, so there are some new faces in the competition.
Federer opens on Sunday afternoon against Jack Sock of the United States, while third seed Alexander Zverev of Germany plays Marin Cilic of Croatia.
Austria's Dominic Thiem plays Grigor Dimitrov of Bulgaria on Monday.