New york - 21. august: der sechsmalige Grand-Slam-Champion novak djokovic trainiert für unser open 2014 im billie jean king national tennis center am 21. august 2014 in new york - Stockfoto & -bild

NEW YORK - AUGUST 24: Six times Grand Slam champion Novak Djokovic practices for US Open 2014 at Billie Jean King National Tennis Center on August 24 , 2014 in New York

NEW YORK - AUGUST 24: Six times Grand Slam champion Novak Djokovic practices for US Open 2014 at Billie Jean King National Tennis Center on August 24 , 2014 in New York

NEW YORK - AUGUST 24: Six times Grand Slam champion Novak Djokovic practices for US Open 2014 at Billie Jean King National Tennis Center on August 24 , 2014 in New York

NEW YORK - AUGUST 22, 2018: 13-time Grand Slam champion Novak Djokovic of Serbia practices for the 2018 US Open at Billie Jean King National Tennis

MIAMI GARDENS, FLORIDA - MARCH 27, 2023: Francisco Cerundolo of Argentina in action during round of 32 match against Felix Auger Aliassime of Canada at 2023 Miami Open at the Hard Rock Stadium in Miami Gardens, Florida, United States

NEW YORK - AUGUST 24: Six times Grand Slam champion Novak Djokovic practices for US Open 2014 at Billie Jean King National Tennis Center on August 24 , 2014 in New York

NEW YORK - AUGUST 22, 2018: 13-time Grand Slam champion Novak Djokovic of Serbia practices for the 2018 US Open at Billie Jean King National Tennis

AUGUST 26, 2014: Professional tennis player Kei Nishikori from Japan during US Open 2014 match against Wayne Odesnik at Billie Jean King National Tennis Center in New York

NEW YORK -SEPTEMBER 6, 2016: Grand Slam champion Mike Bryan in action during US Open 2016 quarterfinal doubles match at Billie Jean King National Tennis Center in New York

NEW YORK - SEPTEMBER 3, 2017: Professional tennis player Lucas Pouille of France in action during his US Open 2017 round 4 match at Billie Jean King National Tennis Center

NEW YORK - AUGUST 31, 2015: Professional tennis player Kei Nishikori of Japan in action during first round match at US Open 2015 at Billie Jean King National Tennis Center in New York

AUGUST 26, 2014: Professional tennis player Kei Nishikori from Japan during US Open 2014 match against Wayne Odesnik at Billie Jean King National Tennis Center in New York

FLUSHING, NY - AUGUST 21: Professional tennis player Fernando Verdasco practices for US Open at Louis Armstrong Stadium at Billie Jean King National Tennis Center on August 21, 2012 in Flushing, NY.

NEW YORK - SEPTEMBER 6, 2015: Professional tennis player Jo-Wilfried Tsonga of France in action during his round four match at US Open 2015 at National Tennis Center in New York

NEW YORK -SEPTEMBER 5, 2016: Professional tennis player Kei Nishikori of Japan in action during his round four match at US Open 2016 at Billie Jean King National Tennis Center in New York

NEW YORK - AUGUST 22, 2018: 13-time Grand Slam champion Novak Djokovic of Serbia practices for the 2018 US Open at Billie Jean King National Tennis

FLUSHING, NY - AUGUST 24: Professional tennis player Ricardas Berankis practices for US Open 2013 at Billie Jean King National Tennis Center on August 24, 2013 in Flushing, NY

NEW YORK- SEPTEMBER 3, 2016: Twelve times Grand Slam champion Novak Djokovic of Serbia practices for for US Open 2016 at Billie Jean King National Tennis Center in New York

NEW YORK - AUGUST 22, 2018: 13-time Grand Slam champion Novak Djokovic of Serbia practices for the 2018 US Open at Billie Jean King National Tennis

NEW YORK - AUGUST 30, 2016: Professional tennis player Kei Nishikori of Japan in action during his first round match at US Open 2016 at Billie Jean King National Tennis Center in New York

NEW YORK - AUGUST 22, 2018: 13-time Grand Slam champion Novak Djokovic of Serbia practices for the 2018 US Open at Billie Jean King National Tennis

FLUSHING, NY - AUGUST 21: Professional tennis player Fernando Verdasco practices for US Open at Louis Armstrong Stadium at Billie Jean King National Tennis Center on August 21, 2012 in Flushing, NY.

NEW YORK - AUGUST 24: Professional tennis player Janko Tipsarevic practices for US Open 2013 at Billie Jean King National Tennis Center on August 24, 2013 in New York

FLUSHING, NY - AUGUST 25: Grand Slam champion Andy Roddick practices for US Open at Louis Armstrong Stadium at Billie Jean King National Tennis Center on August 25, 2012 in Flushing, NY.

NEW YORK - SEPTEMBER 6, 2016: Professional tennis player Lukas Poulle of France using Tweener during round four match at US Open 2016 at Billie Jean King National Tennis Center

NEW YORK - SEPTEMBER 2, 2018: Professional tennis player Dominic Thiem of Austria in action during his 2018 US Open round of 16 match at Billie Jean King National Tennis Center