Porto could be relegated to the second division after being formally notified they and president Pinto da Costa are under investigation of match-fixing in the 2003/04 season.
That year saw arguably Jose Mourinho's greatest triumph as he lead the Portuguese side to the league and Champions League double before moving to Chelsea.
A brief statement on the club's website www.fcporto.ptread: "FC Porto and their president have been notified by the Portuguese Professional Football League (LPFP) of the accusations and investigations concerning matches between FC Porto and Estrela da Amadora, and Beira Mar and FC Porto."
Porto won the former 2-0, while the match at Beira ended in a goalless draw, but both results are under investigation over allegations of corrupting the referees.
The case — referred to in Portugal as "the golden whistle" — has been monitored for nearly four years, with close collaboration between the LPFP and the Portuguese legal system.
Porto have sent the accusations to their lawyers and have five days to submit their defence.
The club could be docked three points from this campaign — in which they currently lead Benfica by 16 points — or face relegation to the second division.
Da Costa could face a ban of between two to 10 years if found guilty of corruption or six months to two years for attempted corruption.
The Porto president was charged in 2005 for three offences of active corruption and corrupt practices, but was released because of a lack of evidence.
