"We have started to work together in September 2013 and we had a lot of success during that period, especially winning the US Open in 2014.
"It was a huge privilege to work with Goran, I enjoyed our work all this time and Goran helped me to reach many goals.
"Unfortunately, the road we were sharing on this journey is separating and I wish only the best for Goran in the future."
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The pair last worked together at Wimbledon, where Cilic surrendered a two-set lead to lose to Roger Federer in the quarter-finals.
Cilic was part of Croatia's 3-2 comeback win over the United States in the Davis Cup quarter-finals on Sunday.
(Reporting by Ian Rodricks in Bengaluru; Editing by Ian Ransom)
