Steffon Armitage insists he has done nothing wrong despite the "stress" of his "abnormal" doping test result.
The Toulon flanker was informed on Wednesday that he had tested positive for the prohibited substance morphine after the Top 14 final defeat by Toulouse on June 9.
Toulon have issued a statement insisting the result was caused by approved painkillers and anti-inflammatories prescribed for back pain.
The French club stress that the 26-year-old "has absolutely not taken any illegal substance to improve his performance" and that the morphine is a natural by-product of the painkillers.
And Armitage, who has played five times for England, said in a press conference broadcast on the club's website: "It's a bit stressful, especially for my family in England.
"But I will keep my head held high because I have done nothing wrong.
"I know that everything will soon be sorted, that I will be able to forget about this and come back stronger."
According to reports in France, Armitage will appear before the FFR anti-doping commission on August 21 and has been provisionally suspended pending the hearing.
Toulon's statement this morning read: "Toulon Rugby Club received a letter this Wednesday, July 25, 2012, from the French Rugby Federation reporting an 'abnormal' result from an anti-doping test taken by Steffon Armitage after the Top 14 final on June 9 at the Stade de France.
"Before the game, Steffon Armitage took two tablets of paracetamol codeine, a medicine strictly authorised by the French Agency for the Fight against Doping (AFLD).
"Having suffered with back pain in the week leading up to the game, Steffon Armitage was given anti-inflammatories as well as paracetamol codeine (two to four tablets per day) for these pains. All of the medicines administered are authorised by the AFLD.
"The presence of morphine in Steffon Armitage's urine sample is explained by the fact that 10% of this medicine (paracetamol codeine) is converted naturally into morphine.
"Steffon Armitage has absolutely not taken any illegal substance to improve his performances, but solely a medicine strictly authorised by the AFLD and well known to all."
Armitage won his first international cap against Italy in the 2009 RBS 6 Nations, following his brother Delon into the team - the first pair of brothers to represent England since wingers Rory and Tony Underwood.
But he has not featured since a game against the same opposition the following year and moved to France in 2011 after five seasons with Irish, who he joined after coming through Saracens' academy.