World number 15 Marin Cilic is reportedly being investigated by the International Tennis Federation over an alleged failed drugs test.
Reports in Cilic's native Croatia have claimed that the 24-year-old failed a test at the BMW Open in Munich in April this year.
The findings are said to have discovered that an "incautious use of glucose" was found in his system just two weeks after he passed a doping test at the Monte Carlo Masters, according to The Telegraph.
Cilic, who was beaten by Andy Murray in the final of the AEGON Championships at Queen's, has not played since he pulled out of Wimbledon with a knee injury ahead of the second round.
