The Twenty20 Cup quarter-final between Durham and Yorkshire was tonight postponed after the England and Wales Cricket board revealed they are investigating allegations the visitors fielded an ineligible player during the group stage.
In the crucial match against Nottinghamshire at Trent Bridge on June 27, Yorkshire's line-up contained Azeem Rafiq.
The ECB received an allegation the player was not eligible to play and this morning the board's legal advisors confirmed Rafiq was ineligible.
There is now the prospect of the Nottinghamshire-Yorkshire match being replayed.
A statement from the ECB said: "The Twenty20 Cup quarter-final between Durham and Yorkshire was postponed after the England and Wales Cricket Board today received allegations that Yorkshire had fielded an ineligible player in a crucial Twenty20 group match.
"In a Twenty20 group match on June 27 at Trent Bridge between Yorkshire and Nottinghamshire, Yorkshire fielded Azeem Rafiq, who is alleged to be an unqualified cricketer.
"The match between Yorkshire and Nottinghamshire decided which team qualified for the Twenty20 Cup quarter-finals.
"As soon as the allegations were received by the ECB it was agreed to convene a panel of the Cricket Disciplinary Commission.
"After investigation this morning the board's legal advisers confirmed that the player was not eligible to be registered as a qualified cricketer.
"ECB made it clear to both counties that in view of the alleged ineligibility of Azeem Rafiq, it was possible the panel could order the replay of any match or matches which could affect any quarter-final.
"The ECB are convening a meeting of the panel as a matter of urgency so that any relevant matches will be played before Twenty20 finals day at Southampton on July 26."