2014 United States Open champion Marin Cilic is yet to kick off his 2015 season on the professional tour. The Croatian withdrew from the Brisbane International and the Australian Open with a shoulder injury, and now it appears that he is still unfit to return to the ATP World Tour.

The two-time defending champion was forced to withdraw from his hometown tournament in Zagreb, Croatia – one that he has won four times overall.

‘My injury is improving, but my arm still has not healed enough, so I will have to continue with the treatment for a while longer.”

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The reigning US Open champion is a former semi-finalist at the Australian Open (2010), where he lost to tournament runner-up Andy Murray. After only playing a few matches at the IPTL during the off-season, it now appears that the shoulder injury that limited his playing then has only gotten worse over the following month.

The Zagreb Indoor is set to begin on Monday, Feb. 2nd.