Shakhtar Donetsk captain Darijo Srna has tested positive for a banned substance and will miss next week's Champions League meeting with Manchester City.
The 35-year-old right-back, Croatia's most capped player with 134 appearances, has denied intentionally doping, but has opted to take a break from playing to focus on clearing his name.
Srna said he was notified on Monday by Ukraine's national anti-doping centre (NADCU) that he had failed an out-of competition test in March.
He said in a statement on the Shakhtar website: "First and most important, I would like to make it clear that I have never knowingly or intentionally taken any prohibited substance, nor unfairly intended to gain a competitive advantage.