Toulon flanker Steffon Armitage has produced an "abnormal" doping test result - but his club insist he has not taken a banned substance.

The 26-year-old, who has played five times for England, was informed yesterday of the issue arising from a test taken after the Top 14 final at the Stade de France on 9 June.

But a club statement released this morning insists the result was caused by approved painkillers and anti-inflammatories prescribed for back pain and that Armitage "has absolutely not taken any illegal substance to improve his performance".

Toulon revealed the prohibited substance present in Armitage's test was morphine, but said this is a natural side-effect of the painkillers taken by the former London Irish player.

The statement, issued on the club's official website, read: "Toulon Rugby Club received a letter this Wednesday, 25 July, 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 9 June at the Stade de France."

The statement continued: "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."