Shakhtar Donetsk captain Darijo Srna says he will not play again until he clears his name after reportedly failing a doping test.
The 35-year-old former Croatia captain revealed he had been informed by Ukraine's anti-doping body that he reportedly failed an out-of-competition test on March 22 this year.
Srna insists he has never knowingly taken a banned substance and is cooperating fully with authorities in a bid to clear up the matter.
In a statement released via Shakhtar's official website on Friday, he said: "On September 18 2017, I was notified by the National Anti-Doping Centre of Ukraine (NADCU) that a prohibited substance was reportedly found in an out-of-competition sample I had provided on March 22 2017.
"Firstly and most importantly, 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. I am investigating the possible source of the substance and am cooperating fully with NADCU in this respect.
"In order to focus on my defence and avoid any undue distractions for the team, I have made the decision to refrain myself from playing until the ongoing legal proceedings have been resolved. I will now be focused entirely on clearing my name and reputation.
"Over the course of my entire career I was always under the impression that I had to persistently prove myself over and over again.
"Today is another such example when I will once again prove that everything I have accomplished, thus far, both in my life and my professional career, has been achieved solely through hard work, integrity, discipline, and honesty above all. These are the principles which were instilled in me by my late father, and are the same principles by which I am raising my own children today.
"Due to the confidentiality of the legal proceedings, I am not able to comment any further at this stage.
"I would like to thank first of all my family, the club and our loyal fans for their continual support in this matter and look forward to being back on the pitch as soon as possible. This is not the end of my career, I can promise you that!"
Srna has enjoyed huge success since joining Shakhtar from Hajduk Split in 2003, winning nine top-flight titles in Ukraine and the 2008-09 UEFA Cup among a host of honours.
He won a record 134 caps for Croatia before announcing his international retirement following Euro 2016.