PLAYERS' chief Gordon Taylor last night warned Abel Xavier his career was hanging in the balance following last month's failed drugs test.

The Middlesbrough full-back has protested his innocence after his A-sample came back positive following the UEFA Cup clash with Xanthi.

He claimed there was an "entirely harmless explanation" for a banned substance being present in his system.

UEFA officials will meet on Monday to begin analysing the B-sample that was taken at the same time and, if that too includes a prohibited drug, Xavier can expect a lengthy ban.

Middlesbrough officials, who will fly to Zurich this morning for tomorrow's UEFA Cup group-stage game with Grasshoppers, have so far failed to comment on the situation.

But, with the 32-year-old having signed only a one-year deal when he moved to Teesside in August, a suspension of six months or more is almost certain to spell the end of his time with Boro.

It could even bring about the end of the Portuguese international's career.

As chief executive of the Professional Footballers' Association, Taylor is responsible for making sure his members are aware of football's strict drug regulations.

And, after recently issuing a new set of guidelines to players, club doctors and physiotherapists, he has warned Xavier to fear the worst.

"There will be a test of the B sample but that normally is consistent with the first," said Taylor. "If you're taking anything at all you have to OK it with the club because the authorities are taking a much stricter line.

"They're looking to take stronger action now.

"It could well be - unless there's a very substantial reason as to why this is positive that is to be understood - anything from six months to two years.

"There's a general disapproval of performance-enhancing drugs and that's why there's not a lot of sympathy there with the sanctions.

"I know there are very strong moves from FIFA and WADA. We're talking about a minimum two years, which would virtually finish a career."

Xavier is understood to have tested positive for a non-recreational drug, making him the first Premiership player to have been caught with a performance-enhancing substance in his system.

Middlesbrough are standing by him until the result of his B-sample is known, but will be aware of Chelsea's stance after Adrian Mutu tested positive for cocaine.

The London club sacked the Romanian international after he was banned from football for seven months.

"We mustn't pre-judge that he is going to be found guilty," added Taylor. "We don't know that until the result of tests on his B-sample is known.

"But we have had a recent incident when Adrian Mutu was found guilty of taking drugs and Chelsea terminated his contract after he tested positive for a social drug."

While other sports have seen a succession of positive tests, footballing drug cheats remain few and far between.

Taylor accepts that Xavier's positive sample is a cause for concern, but maintains the sport is cleaner than most.

"Football sometimes gets accused of being too soft," he said. "I don't think we are.

"We've extended tests regularly since 1978.

"We like to think the game is relatively clean. The vast majority - hardly any at all - have been performance enhancing, but one can be one too many.

"We've got an image to protect and an image for youngsters coming into the game.

"When you see what happens in other sports we don't want that in football."

Xavier, who is currently out of the country, will now undergo a series of tests on his body fluids and tissues that he hopes will prove he did not intentionally take a banned drug.

He is maintaining that a range of American supplements he was taking to treat a virus could have contributed to a positive test. He accepts, however, that convincing FIFA of his innocence is not going to be an easy process.

His statement said: "Given the fact that the anti-doping regulations establish a purely objective responsibility (the athlete is guilty as of the moment when the most minor trace of a prohibited substance is found in his body), I currently have - and this is not easy - to furnish scientific and factual proof to establish that if a prohibited substance is found in my body this is by no means because I would have had the intention to 'dope' myself. I have never had this intention."

* Ugo Ehiogu is expected to be back in the Middlesbrough squad that travels to Switzerland this afternoon.

The former England international has missed the last three games with a groin problem.

Xavier's place at right-back is likely to be taken by Stuart Parnaby, after the full-back deputised for the Portugal international in Saturday's 1-1 draw with Portsmouth.

Read more about Middlesbrough here.