London - Roger Federer has backed rising Japanese star Kei Nishikori to fulfil his potential by breaking into the top 10 next year.
Nishikori has been regarded as one of the sport's brightest young talents since he became the youngest player to finish in the top 100 in 2008.
He won his first ATP event aged 18 but was sidelined by injury for much of 2009 and is only now making his way back into the higher echelons of the rankings.
The Shimane-born Nishikori reached a career-high ranking of 24th earlier this month after impressive runs to the semi-finals of the Shanghai Masters and the Basel final.
His path to the last four in Shanghai included a victory over world number six Jo-Wilfried Tsonga, but it was his form in Basel that really caught Federer's eye.
Nishikori, now based in Florida, came from a set down to beat world number one Novak Djokovic and also knocked out former Wimbledon finalist Tomas Berdych before losing to Federer in the final and the Swiss believes the 21-year-old is ready to make a breakthrough.
"I knew he had great potential from the first time I hit with him when he was 17," Federer said. "I always saw a very talented player in front of me every time I played with Kei.
"For me it was nice to see the breakthrough he did in Shanghai and then also in Basel, using the wild card to his advantage and moving all the way to the final.
"Beating Djokovic, the season he had; Berdych, also the great season he had, was really nice to see.
"Playing him in the finals like this is special because I know Japan is a country that gets very excited about a player like Kei."
While Nishikori is yet to get past the fourth round of a Grand Slam, Federer is confident it is only a matter of time before the youngster gets the big wins that will transform his career.
"I'm sure he's going to be a wonderful player," Federer said.
"Only the future will tell if he's going to move into the top 10 or top five.
"But I definitely think he has the potential and he's a wonderful player and a very nice guy."
While Nishikori has a bright future ahead of him, Federer has reached the point in his magnificent career when he can start to think about his legacy.
He already holds a record 16 Grand Slam titles and is only two wins away from a record sixth title at the ATP World Tour Finals after cruising into the semi-finals at the season finale.
Federer, who plays his semi-final on Friday, will finish the year without a Grand Slam crown for the first time since 2002, but he believes another title at the O2 Arena will be the perfect response to the critics who have written him off.
"I guess I do play for a little bit of the legacy and the history, you know, the record books, all that stuff," said Federer, who would also equal Ivan Lendl's record for 39 matches won at this event if he lifts the trophy on Sunday.
"I'm surprised how well it's gone always at the World Tour Finals level for me, because these are maybe almost the toughest and most dangerous matches to play during the year.
"It's best-of-three against fellow top 10 players indoors, where a few shots usually decide the outcome of the match."