Novak Djokovic of Serbia kisses the winners trophy after defeating Roger Federer of Switzerland in their men's singles final tennis match at the Wimbledon Tennis Championships, in London July 6, 2014.
Athletes with Abusive Coaches Tend to Cheat More. Reuters

With Rafael Nadal's wrist injury, Novak Djokovic and Roger Federer become the top two contenders for the US Open championship in Flushing Meadows. Still, tennis big guns should also be worry of an emerging threat from Asia. His name is Kei Nishikori.

After a season that saw him pulling the rug on elite opponents, the 24-year old Nishikori is ready for a big challenge and his next target are no other than tennis fabled 'Big Four.'

The world's no.11 is oozing with confidence entering the North American hard-court season, as he looks to make some noise on a surface dominated once again by players named Djokovic, Nadal, Federer and Murray.

Nishikori, who boasts career victories against Djokovic and Federer, believed he has a shot at becoming tennis next big thing by breaking the disparity between the elites and the up-and-coming stars like him.

He admitted that it's going to be a hard task beating top-5 opponents, but his fearlessness to take on these big players would allow him to take his game to another level.

"There's still a big difference in the top five or so. They don't miss easy shots and don't give you easy points to win a game," Nishikori said Tuesday via Sportal.com. For me, I don't feel any fear to play them any more after beating them a couple times. I have more confidence now to play the top guys."

Nishikori defeated Federer twice in their four head-to-head matches with the latest victory against the future Hall of Fame coming in the quarterfinal round of the Miami Masters. Federer, meanwhile, exacted some revenge against the Japanese by beating him in straight sets in the semifinal round at Gerry Weber Open in Halle.

Meanwhile, Nishikori's solitary win against Djokovic happened few years ago at the 2011 Swiss Indoors Basel Open. He also nearly defeated Nadal in Madrid, leading 2-6 6-4 3-0 before he was forced to retire with a back injury

Former Grand Slam winner Michael Chang has been the driving force behind the Japanese's surge this year. The two has been training hard for the past two weeks, and Nishikori believed he's in fine form for big tournaments ahead.

"I feel very strong," he added. "Physically I'm ok. I had a great two weeks of training. Everything is ready for the US Open."

Nishikori is currently competing in Washington at the Citi Open and scheduled to play at the Rogers Cup, Cincinnati Master and the US Open championship.

For more Roger Federer, Novak Djokovic and Kei Nishikori news, read more at IBT Sports