The 26-year-old Brazil left-back was born in Sao Paulo and qualifies to play in the Premiership only by claiming Portuguese citizenship, which gives him the employment rights of any European Union citizen.

He would not qualify for a work permit to play in England as he has not played enough games for Brazil.

But his right to a passport of convenience is thrown into doubt by revelations that Lisbon's Ministry of Justice, which holds a register of all Portuguese citizens throughout the world, has no record of Silvinho.

Alberto Manuel Avelino, the civil governor of Lisbon who has responsibility for passport applications, said: 'Anyone with a Portuguese passport must first be regis-tered as a Portuguese citizen. Then they can receive an identity card and only then a passport.'

He confirmed that details of all Portuguese passport holders are held on the central registration computer at the Ministry of Justice. While registration officials confirmed the right of two other Premier-ship Brazilians to hold Portuguese citizenship, Emerson Thome of Sunderland and Arsenal's Edu, Silvinho has failed the test.

His full name, Silvio Mendes Campos Junior, and his date of birth (April 12, 1974) were entered into the central computer with a variety of combinations and spellings but no record could be found of his registration.

Similarly, Lisbon's passport office, which has a register of all passports issued out of Portugal, could find no record of him, even though he has carried a Portuguese passport since he arrived in England in June 1999.

Details for £6 million Edu, who originally tried to enter England with a forged Portuguese passport, were found to have been registered at Portugal's consulate in Sao Paulo, Brazil. Thome's citizenship was confirmed at the passport office.

The revelations over Silvinho are potentially a huge embarrassment for Arsenal and their vice-chairman David Dein, who holds the same post at the FA. Arsenal have been embroiled in a series of passport investigations involving Edu and their Lithuanian signing, Tomas Danilevicius, who was able to play in England only after acquiring a Greek passport.

If Silvinho's passport is now proved to be bogus, it could cost Arsenal Premiership points and result in sanctions from UEFA. They could even be thrown out of the Champions League as punishment for fielding an ineligible player. Premiership teams are permitted to play only three non-EU nationals in their team.

With Silvinho registered as a Portuguese player, it has allowed manager Arsene Wenger to include players such as Croatia's Davor Suker, Ukrainian Oleg Luzhny and Argentine Nelson Vivas in the same team. Vivas now has a Spanish passport but he obtained it only last year.

Danilevicius has played in three games for Arsenal while Silvinho has turned out 75 times since his arrival.

Last season, West Ham were forced to replay a Worthington Cup quarter-final because they fielded an ineligible player in Manny Omoyinmi and Arsenal's Premiership rivals will expect similar treatment to be meted out to the north London club to avoid accusations of bias.

The FA will be pressed to investigate the conduct of their own vice-chairman after Arsenal's record of signing players with questionable qualifications. Dein enjoys a close relationship with FA chief executive Adam Crozier.