London: Middlesbrough defender Abel Xavier failed a drugs test after the Uefa Cup tie against Greek club Xanthi on September 29, the Premier League club said on Monday.
Fifa have suspended the 32-year-old from all competitions pending the outcome of a disciplinary investigation.
Middlesbrough said on their website they were not in a position to make any further comment at the moment but understood Xavier would make a press statement on Tuesday.
The former Portugal international joined Middlesbrough at the end of August on transfer deadline day after a spell in Serie A with AS Roma.
He has played previously for Bari, German club Hanover 96 and for Everton and Liverpool in England. He also had a loan spell with Galatasaray in Turkey.