Roger Federer of Switzerland
Roger Federer of Switzerland arrives to play Kei Nishikori of Japan in their tennis match at the ATP World Tour finals at the O2 Arena in London November 11, 2014. Reuters

Without a shadow of doubt, Roger Federer said that Rafael Nadal will be able to win big titles again and climb up the world rankings when he returns. Nadal recently had undergone appendectomy that forced him to withdraw in the remaining tournaments of the season. Nadal is currently recovering from the surgery.

The Spaniard missed a lot of tournaments this season, including the US Open due to a wrist injury and he has only played seven matches since competing in the Wimbledon Championships. Despite that, Federer is certain that his rival will come back strong.

In a news article by USA Today, Federer said that he is well-aware of Nadal's great tennis skills and he expects that Spaniard to be back in his old winning form.

"I think, he'll be playing for the biggest titles in sport and maintaining his ranking and moving up again," Federer uttered. "I think that's what he expects from himself and that's what I hope we'll see again."

According to USA Today, they tried to reach out to Nadal for a statement. However, the third-ranked athlete opted not to comment on the story.

Meanwhile, Federer defeated Andy Murray in his third round-robin match at the Barclays ATP World Tour Finals staged at the O2 Arena in London on November 13. Federer only needed 56 minutes to secure his straights sets victoru, 6-0, 6-1, over the Scot.

Speaking after the match via ESPN, Federer said that his confidence has contributed to his victory. He said he went into the match feeling "qualified and relaxed." Even before Federer played against Murray, he has already secured a semifinals berth when Japanese debutant Kei Nishikori defeated David Ferrer, 4-6, 6-4, 6-1. Ferrer is the first alternate in the event. Milos Raonic of Canada was forced to pull out due to an injury.

Federer leads Group B, while top seed Novak Djokovic leads the other group. Djokovic is close to ending the season as World No. 1 if he wins against Tomas Berdych in his next match.

Federer has now equaled Ivan Lend's in terms of semifinals appearances in the ATP World Tour Finals. Both players boast a record of 12 semifinals appearances in the season-finale, where Federer is a six-time titlist having had won in 2003-2004, 2006-2007, and 2010-2012.