This followed an anti-doping test that took place after Oxford's fixture against Cheltenham Town on 3 January 2015.
In respect of this breach, at a Regulatory Commission hearing that took place on 4 June, it was held that there was no intention on the part of Mr Dunkley to enhance his sporting performance and Mr Dunkley was issued with a warning and reprimand, and ordered to be subject to target testing for a period of two years. The FA also agreed in this case that there was no intention on the part of Mr Dunkley to enhance his sporting performance.
The full written reasons for the decision can be found here.
Mr Dunkley has a right to appeal the decision.