Belfast athlete Gareth Turnbull is facing a possible two-year ban after a drugs test showed up higher than normal levels of testosterone.
Turnbull won the 1500m at last weekend's NI Championships
The doping charge relates to an out-of-competition test which was conducted on 30 September last year.
A spokesman for the 27-year-old told BBC Sport that the athlete "emphatically denied any wrong doing".
"He is absolutely determined to vindicate himself in the weeks and months ahead," added the spokesman.
Turnbull is understood to have had several tests before and after the 30 September test which showed normal testosterone levels.
The runner is now certain to ask the Irish Sports Council to test the B-sample of the urine that he submitted on 30 September.
However, the Belfast athlete has been provisionally suspended and the timing of the shock news means his hopes of competing in this year's European Championship now seem remote.
Turnbull's case will now be referred by the Irish Sports Council to a disciplinary panel who will make a judgement.
Guilty verdicts in these kind of doping cases usually mean a two-year ban although there would be the option of making an appeal to the Court of Arbitration for Sport in Switzerland.
Turnbull has a 1500m personal best of 3:36.60 set in 2003, the year that he competed in the World Championships.
His career has been severely affected by injury but he showed promising signs of a return to form last weekend when he impressively won the 1500m at the Northern Ireland Championships.