London (AFP) - Kei Nishikori said Friday he was "lucky" to be at the ATP Finals after clawing his way up the rankings following a lengthy injury lay-off to reach for the elite eight-man event in London.
The Japanese player qualified for the tournament, which starts at the O2 arena on Sunday, as a result of the withdrawal of Juan Martin del Potro due to a right knee injury.
"Lucky for me," he said. "I couldn't really see that happening at the beginning of the year. Maybe until Monte Carlo I was playing terribly and didn't feel like I had any confidence and I wasn't playing good tennis at that time."
Nishikori returned to action in January after a five-month absence due to a right wrist injury but fell to number 39 in the ATP rankings in April, his lowest position since 2011.
The 28-year-old said his confidence increased after the French Open and Wimbledon -- he reached the semi-finals at the US Open, where he lost to Novak Djokovic.
"I'm really happy that I've been playing really good tennis for the last couple of months after the US Open and I hope I can have one more good week next week here," he said.
Nishikori opens his tournament against world number three Roger Federer and admitted it would be tough after two recent losses against the Swiss.
"I lost to him in Shanghai and Paris recently so I've got to really make adjustments on Sunday but I always enjoy playing Roger," said Nishikori.
Nishikori is making his fourth appearance at the season finale, having reached the semi-finals in 2014 and 2016.