Welsh athlete Gareth Warburton has been provisionally suspended from all competition after being charged with anti-doping violations.
Warburton, 31, who is an 800m runner, was expected to compete in his third Commonwealth Games in Glasgow, but will now miss the event.
"The news of this anti-doping rule violation has come as a great shock to me," he said in a statement.
"From the outset, I would like to state that I have not knowingly taken any banned substance."
UK Athletics has confirmed the athlete can appeal against the provisional suspension, something Warburton is eager to do.
"I recognise that the responsibility for this situation lies with me and I’m committed to working with UK Anti-Doping and will fully cooperate in the legal process.
"As a professional athlete, I have always supported and have been an advocate of clean sport. Nothing has changed in this regard."
Warbuton finished fourth in Delhi four years ago and would have been hoping to challenge for a medal when this summer's Games begin in Glasgow on July 23.
He has a personal best of 1:44.98, which he set in a Diamond League meet in Oslo two years ago. A time similar to that may would have seen him compete well in Scotland, but Warburton will have to wait another four years if he wants a chance at Commonwealth success.
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