Rafael Nadal cast doubt Thursday on whether he could win another Grand Slam after his long reign as French Open champion ended and he slid down the rankings during the worst year of his career.

The 29-year-old Spaniard said he was working hard to return to form and was happy with the way the year ended after a resurgence at the World Tour Finals in London last month.

But asked whether he could clinch another major title to add to the 14 Grand Slams he has already accumulated, Nadal was unconvinced.

"I don't know when that will happen and I don't know if that's going to happen," he told reporters in New Delhi.

"The only thing I know is I'm working very hard to try to get the opportunities."

Nadal was speaking after hitting balls with youngsters during a coaching session in the Indian capital, where he plans to open an academy for talented players.  

Nadal sunk to world number 10 this year after losing at the French Open quarter-final stage, before suffering early exits from Wimbledon and the US Open.

But the Spaniard, who has been plagued with injuries and last year had surgery to remove his appendix, rallied to finish at world number five.

"This year has been not the best season," he said.

"(But) In the last three months, I finished much better and I'm happy the way I'm playing now. I need to keep going the same way that I finished the 2015 season."

Nadal is in Delhi to play in the International Premier Tennis League (IPTL), which promotes a shortened, speeded-up version of the game that organisers say is more television-friendly than the traditional format.

The IPTL, which began in Japan this month, had a stop in Manila earlier this week and there are also dates in Dubai and Singapore.
Source: AFP