Sale prop Eifion Lewis-Roberts could be banned for two years after testing positive for morphine and pseudoephedrine.
Lewis-Roberts failed a test which took place after last season's Top 14 final between Toulon - his former club - and Toulouse.
Four weeks ago a B sample was tested, seven months after his last match for Toulon, the prop having joined Sale in the summer.
Toulon flanker Steffon Armitage also tested positive after the French final but he was not banned.
A disciplinary panel accepted that the morphine found in his sample came from two anti-inflammatory tablets he had taken before the match and the former London Irish man had been open about taking the tablets on his dope test form.
A Sale spokesman said: "The matter is in the hands of the Rugby Football Union and Premiership Rugby.
"Eifion has been rested for the last few weeks but he is available for selection for our match at London Welsh on Sunday."
Toulon president, Mourad Boudjellal expects Lewis-Roberts' case to end the same way as Armitage's.
"The player is not a drugs cheat," he said. "He took a product to relieve pain he was in and that is all there is to it."