ATP Finals: Nadal still unsure over injury in London
The 19-time grand slam champion has never won the ATP Finals, finishing as runner-up twice, but won't be risking further injury problems in London.
Rafael Nadal revealed he has started serving "very slowly" and will "see how things go" as he delivered a mixed injury update ahead of the ATP Finals.
The US Open winner is in London ahead of the year-ending tournament as he recovers from an abdominal tear sustained last Saturday.
Nadal had to pull out of his Paris Masters semi-final against Denis Shapovalov after experiencing discomfort in the warm-up.
He underwent an MRI in Mallorca and declared he was planning to play the ATP Finals on Tuesday.
Nadal still indicated his determination to play in a further update provided on Friday, but explained he was taking things slowly.
He wrote on Twitter: "Update? Ok, I'm in London happy to be here. Taking it day by day after Paris (small abdominal tear).
"I need to see how things go, started serving [on Thursday] very slowly. Right now the main goal is to be ready on Monday following the protocols that the doctor gave me."
Nadal, 33, is a 19-time grand slam champion but has never won the ATP Finals, finishing as runner-up twice. He had to withdraw from last year's event due to another abdominal problem he picked up in Paris.
The Spaniard has been drawn in Group Andre Agassi this year along with Daniil Medvedev, Stefanos Tsitsipas and 2018 champion Alexander Zverev, who is scheduled to be his first opponent on Monday.
Novak Djokovic will begin the singles tournament with a Group Bjorn Borg match against Matteo Berrettini on Sunday. Roger Federer and Dominic Thiem are the other participants.