"I would reckon the Novak Djokovic group is the tougher one", Becker said, as quoted on the Express.
However, Djokovic and every other tennis star pales in comparison when it comes to Federer's endorsements, with the 37-year-old, named the highest-paid tennis player by Forbes earlier this year for the 13th year in a row, earning $65 million from endorsements. The conditions at the season finale in London are expected to be slightly heavier, but being indoors, with the elements not playing a part, the setting is ideal for Federer's precisely directed weaponry.
This was a decision Nishikori and his team will look back on whatever the outcome is at the Tour Finals next week and know that they made the right call.
The pace at which Federer plays and the rhythm he gets into on fast courts have never been to Djokovic's liking. Overall I'm happy with my game. He has chased only a few tennis records with genuine intent, including the men's mark for Grand Slam singles titles, which Pete Sampras once held with 14 and which Federer now owns with 20.
'I don't want it to move from London, I just feel the concept of this event is it should be the one that travels, ' he said.
The 31-year-old was dumped out of the US Open in the second round.
John Isner, like Anderson, will also be making his debut at the tournament. He reached his first ATP Masters 1000 final in Toronto, and won his first title in Stockholm, as well as reached the fourth round at Wimbledon.
Alexander Zverev and Dominic Thiem, from a generation further below, are still developing. The ATP Finals in London begins on Sunday. "What we have found out over the years is that if you have a couple of great players winning a lot of Majors, the generation that follows usually suffers", he told Sports Illustrated. I just feel this is a great leverage and opportunity to promote tennis all around the world.
With more players still to be announced over the coming weeks, the tournament is shaping up to be one of the most well rounded in recent times with strong fields for both the Women's and Men's weeks already confirmed.
Fast forward to a year ago and after cutting his season short in August after scans revealed a tear in one of his tendons, Nishikori was forced to ask himself the question that no top sports athlete in their prime ever was to contemplate - retirement.