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NEW YORK, NY – SEPTEMBER 4: Gunter Bresnik, coach of Dominic Thiem of Austria during day 9 of the 2018 US Open at Arthur Ashe Stadium of USTA Billie Jean King National Tennis Center on September 4, 2018 in Flushing Meadows, Queens, New York City. (Photo by Jean Catuffe/Getty Images)

NEW YORK, NY - SEPTEMBER 4: Gunter Bresnik, coach of Dominic Thiem of Austria during day 9 of the 2018 US Open at Arthur Ashe Stadium of USTA Billie Jean King National Tennis Center on September 4, 2018 in Flushing Meadows, Queens, New York City. (Photo by Jean Catuffe/Getty Images)

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NEW YORK, NY – SEPTEMBER 05: Gunter Bresnik coach of Dominic Thiem of Austria looks on during his fourth round Men's Singles match against Juan Martin del Potro of Argentina on Day Eight of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 5, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Al Bello/Getty Images)

NEW YORK, NY - SEPTEMBER 05:  Gunter Bresnik coach of Dominic Thiem of Austria looks on during his fourth round Men's Singles match against Juan Martin del Potro of Argentina on Day Eight of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 5, 2016 in the Flushing neighborhood of the Queens borough of New York City.  (Photo by Al Bello/Getty Images)

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LONDON, ENGLAND – NOVEMBER 12: Dominic Thiem of Austria sqpeaks with his coach ?Gunter Bresnik during a practice session during previews for the Barclays ATP World Tour Finals at O2 Arena on November 12, 2016 in London, England. (Photo by Clive Brunskill/Getty Images)

LONDON, ENGLAND - NOVEMBER 12:  Dominic Thiem of Austria sqpeaks with his coach ?Gunter Bresnik during a practice session during previews for the Barclays ATP World Tour Finals at O2 Arena on November 12, 2016 in London, England.  (Photo by Clive Brunskill/Getty Images)

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BARCELONA, SPAIN – APRIL 23: Dominic Thiem from France training with his coach Günter Bresnik during the Barcelona Open Banc Sabadell 66º Trofeo Conde de Godo at Reial Club Tenis Barcelona on 23 of April of 2018 in Barcelona. (Photo by Xavier Bonilla/NurPhoto via Getty Images)

BARCELONA, SPAIN - APRIL 23: Dominic Thiem from France training with his coach Günter Bresnik during the Barcelona Open Banc Sabadell 66º Trofeo Conde de Godo at Reial Club Tenis Barcelona on 23 of April of 2018 in Barcelona.  (Photo by Xavier Bonilla/NurPhoto via Getty Images)

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PARIS, FRANCE – NOVEMBER 1: Gunter Bresnik, coach of Dominic Thiem of Austria during Day 4 of the Rolex Paris Masters at the AccorHotels Arena in Bercy on November 1, 2018 in Paris, France. (Photo by Jean Catuffe/Getty Images)

PARIS, FRANCE - NOVEMBER 1: Gunter Bresnik, coach of Dominic Thiem of Austria during Day 4 of the Rolex Paris Masters at the AccorHotels Arena in Bercy on November 1, 2018 in Paris, France. (Photo by Jean Catuffe/Getty Images)