ABEL Xavier last night insisted he was not a drugs cheat and promised to do everything possible to clear his name after his positive test for a banned substance.

The Middlesbrough full-back, who is excluded from all competitions, has confirmed he failed a drugs test after his side's Uefa Cup match against Greek side Xanthi.

But as he waits for his B sample to be examined next week, the Portugal international said he never knowingly took a banned drug.

"I am convinced that there is a reasonable and entirely harmless explanation for such a positive finding, should it be confirmed by the analysis of the B sample," he said.

"In order to furnish this proof, I'm currently undergoing a number of tests in which certain of my body fluids and tissues are analysed.

"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."

Xavier has been suffering from a virus for most of the past month and is understood to have been taking supplements imported from the US.

Those supplements could have contributed to a positive test, but claiming he was not aware they contained a banned substance will not be enough to see Xavier's ban lifted.

The length of any suspension will depend on what drug was in his system - Uefa have refused to confirm that until his B sample has been examined - but the former Everton and Liverpool defender could face up to two years out of the game.

Given that he turns 33 next month, that would almost certainly spell the end of his career.

Middlesbrough are refusing to make any comment until the result of his B sample is known. The rest of the squad flies to Zurich this morning for tomorrow's Uefa Cup game with Grasshoppers.