World No 15 Marin Cilic is under the radar of the International Tennis Federation for failing a drug test during the BMW Open in Munich in April, it has been reported.
Another Croatia daily Jutarnji List reported that the 24-year-old had 'incautious use of glucose' in his system.
The former Chennai Open champion has not played since pulling out of Wimbledon with a reported knee injury after reaching the second round.
Cilic is a nine-time winner on the ATP Tour and is a former Australian Open semi-finalist and two-time US Open quarter-finalist.
Just last week the ITF had banned Serbian Viktor Troicki for 18 months for flouting doping rules.
The 27-year-old was found guilty of failing to provide a blood sample during a drugs test at the Monte Carlo Masters.
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