US Open 2017: Roger Federer and Rafael Nadal in action on day four

Roger Federer has yet to lose a Grand Slam match this year after his victories at Wimbledon and the Australian Open

Roger Federer will have his fitness tested as he and Rafael Nadal feature on day four of the US Open in New York.

Federer's build-up to the tournament was disrupted by a back injury, and he was taken to five sets in his opening match by teenager Frances Tiafoe.

He will face Mikhail Youzhny in round two on Thursday from about 19:30 BST, before Nadal plays Japan's Taro Daniel in the second night session match.

Top women's seed Karolina Pliskova is also in action on Arthur Ashe Stadium.

She takes on American Nicole Gibbs after Ukraine's Elina Svitolina opens play on the main court at Flushing Meadows against Evgeniya Rodina of Russia.

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Federer, ranked third in the world, is searching for his third Grand Slam title of the year, following his success at the Australian Open in January and Wimbledon in July.

His biggest title rival is Spain's Nadal, who beat Serbia's Dusan Lajovic in his opening match of the tournament.

In the women's draw, French Open champion Jelena Ostapenko, seeded 12th, opens play on Louis Armstrong against Sorana Cirstea, while American 20th seed Coco Vandeweghe begins the night session against Tunisia's Ons Jabeur.

Cincinnati Open champion Grigor Dimitrov, seeded seventh, is second on Louis Armstrong against Aljaz Bedene's conqueror Andrey Rublev before sixth seed Dominic Thiem plays 19-year-old American Taylor Fritz.

Argentina's 24th seed Juan Martin del Potro is second on Grandstand against Spanish world number 148 Adrian Menendez-Maceiras.

Meanwhile, Jamie Murray, Dominic Inglot and Naomi Broady are among the Britons in action as the doubles competitions begin.