I think there is a chance that could mitigate the punishment but not the guilty charge. PED in your blood on matchday is your responsibility, doesnt matter when you took it is my understanding.In which case he might have a legal argument and avoid punishment. This is not an open and shut case as some are assuming.
Will depend on the letter and the spirit of the law and the findings as to when exactly this drug was taken and whether it could reasonably be assumed to not have had an effect on game day.
Club punishment/list management decisions are a seperate issue for later.