Updated 1916 GMT (0316 HKT) December 18, 2013
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Boris Becker has been appointed as Novak Djokovic's new head coach. Becker, who won six grand slams during his career, will start work with the World No.2 ahead of January's Australian Open. Ian Walton/Getty Images
Andy Murray has flourished since teaming up with eight-time grand slam winner Ivan Lendl in 2011. Murray won the 2012 U.S. Open and Wimbledon the following year. Like Lendl, Murray lost his first four grand slam finals. Adrian Dennis AFP/Getty Images
Croatia's Marin Cilic worked with fellow countryman Goran Ivanisevic. Ivanisevic is the only male wildcard to have won the Wimbledon title. Julian Finney/Getty Images
Japan's Kei Nishikori has enlisted the help of former grand slam winner Michael Chang. Former French Open winner Chang will work with Nishikori for 17-20 weeks of the year. MIGUEL MEDINA/AFP/Getty Images
Switzerland's Stanislas Wawrinka has enjoyed success since teaming up with Magnus Norman. Norman, who finished as runner-up at the 2000 French Open and was briefly ranked No.2 in the world, has helped Wawrinka climb to eighth in the world. Glyn Kirk/Getty Images
Maria Sharapova's partnership with Jimmy Connors lasted just one match. The pair worked together for 34 days before moving their separate ways. KENZO TRIBOUILLARD/AFP/GettyImages