The Scotland international Scott MacLeod's returned an irregular drugs test prompting an investigation by the Scottish Rugby Union.
A urine sample given by the 29 year old lock was found to contain abnormally high levels of testosterone and he's been suspended.
MacLeod is pleading innocent and asked for a B sample to be tested but he can't play for or train with Scotland or his club the Scarlets until the investigation is completed.
MacLeod previously tested positive in January, although he was later cleared of any wrongdoing.
On that occasion, a new asthma medicine that contained steroids was found to be the cause of the positive test, and he was acquitted.