Tennis is not just a sport, but a business as well. And like in any other business there are disputes, some of which are resolved amicably while others end up in court. The tennis world has seen many lawsuits in the past. Some that come to mind include Monica Seles suing the German Tennis Federation over her stabbing incident in Hamburg; Canada's Eugenie Bouchard filing a lawsuit against the United States Tennis Association for a fall she suffered in the locker room during the US Open a few years ago; and Alexander Zverev being involved in a legal dispute with his former manager last year.Now, just days after Dominic Thiem won his first Grand Slam title at the US Open, his father Wolfgang Thiem has confirmed that the Austrian's former coach Gunter Bresnik has sued them.Bresnik, who has worked with players such as Boris Becker, Henri Leconte, Patrick McEnroe and Ernests Gulbis in the past, had coached Dominic Thiem from his childhood days right up to 2019. The two parties have known each other since Wolfgang Thiem came to work as a coach at Bresnik’s tennis academy in Vienna in 1997. The pair split last year and while reasons were not given at the time, their differences have become public since then.Indian Wells champion Dominic Thiem and coach Gunter Bresnik suspend relationship as Nicolas Massu steps into role: https://t.co/xVowVXLsU1 pic.twitter.com/TjeN9AQAI0— TENNIS (@Tennis) April 9, 2019Dominic Thiem's father says the situation with Gunter Bresnik is unpleasantAccording to the SPOX website, Wolfgang Thiem spoke on the issue in an interview with ServusTV and said:"It really makes me sad. I was a good friend of Günter Bresnik. We are now so far that he has sued us. The situation is unpleasant, but the story is over for me."Nicolas Massu cheers Dominic Thiem at the 2020 Australian OpenHowever, Dominic Thiem's father did not exactly specify what the legal dispute was about. Since splitting with Bresnik, Thiem has been working with Nicolas Massu, a former world No. 9 in singles and winner of two Olympic gold medals. What a final! @ThiemDomi you showed that dreams can come true when you believe in yourself and fight until the end! Tennis is tough and this match really deserved more than one champion! Congrats also to @AlexZverev and his team for this amazing tournament! Thanks @usopen ❤️NYC🏆 pic.twitter.com/FONwTkRjuB— Nicolas Massu (@massunico) September 14, 2020In the same interview, Wolfgang Thiem said that the decision to change coaches has proven to be correct."He taught him certain things, no question about it. From my point of view, very, very little progress has been made in the last four or five years. You have to also say clearly. He has developed into an independent person, he is the boss of the team. Before he was only the performer, had little freedom. But things have been improving since the separation. "