Here are the profiles of the singles players who will be taking part.
Novak Djokovic is back at No. 1 and continues to have the upper hand as he showed by beating Federer for the fourth straight time by winning a taut, three-set semifinal at the Paris Masters on Saturday. Since the start of Wimbledon, the Serb has compiled a 31-2 record that's reminiscent of his days of dominance. Nadal cited an abdominal injury to close his season early - he hasn't played since the US Open.
Last year's victor of course, was Grigor Dimitrov, who entered the tournament for the first time and walked away with $2,549,000 in prize money earnings following his three-set win over David Goffin in the final.
John Isner, like Anderson, will also be making his debut at the tournament.
The pace at which Federer plays and the rhythm he gets into on fast courts have never been to Djokovic's liking.
Should the Serbian end his year on a high, he will not only earn as much as 1,500 points to further his lead at the top of the rankings, but he could also increase his prize money lead over Federer. "Djokovic, Zverev, Cilic, Isner is a pretty rough one".
Swede Mats Wilander, seven-time Major champion and one of the most serious watchers of modern-day tennis, had an interesting explanation for the lack of breakthrough champions. "I just feel like there was always a couple of guys maybe just a little bit better during that week".
Fast forward to past year 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.
"I won a bunch of tournaments again, played great at the Australian Open". There were Lleyton Hewitt, Andy Roddick, Juan Carlos Ferrero and Marat Safin.
Two recent defeats to Federer will be fresh in Nishikori's mind but he did compete well in their Shanghai and Paris matches so he certainly has what it takes to test the six-time champion. So that makes me feel good about his chances when he does come back.