Federer’s draw became much easier when Nadal announced he was pulling out of the competition on Monday.
The Spaniard is struggling with a stomach injury which he picked up while training at the Paris Masters.
Nadal also underwent ankle surgery on a recurring problem because his season came to a premature end.
But for Federer, he became a top seed which meant he avoided meeting Novak Djokovic in the group stages.
And ahead of the tournament, the Swiss star sent a classy message to his long-term rival, wishing him all the best in his recovery.
“It obviously affected me because I can’t be in a group with Novak,” Federer said of Nadal’s withdrawal.
“It shuffles the entire draw, especially when someone like Juan Martin [del Potro] doesn’t play either.
“He brings excitement, the star power and legendary status – he is going to be missed.
“We have to move on. I wish him the best and a speedy recovery.
“I hope he recovers well and comes back nice and strong next year.
“For us, the tournament is about to start and the focus is on the players who are here and the fans who are going to have a good time seeing some great guys.”
Meanwhile, Federer can win his 100th career at the O2 in London.
But he insists that is not his primary focus.
“I don’t think it matters where I win my 100th as long as I win at some point. That is going to be exciting,” Federer added.
“I think if I won here it is more about winning the World Tour Finals rather than my 100th.
“I think I love playing this event, I always have, ever since I qualified back in 2002. That was a massive highlight in my career, to be in the top eight for the first time in my career.
“Now I am here at the O2, it is a great venue, I have difficult matches and that is my focus here.
“I know it goes hand-in-hand but the focus is on having a good tournament here.
“When the 100 happens it does, hopefully sooner than later but I am happy to wait as well.