UEFA has opened disciplinary proceedings against Dutch striker Ruud van Nistelrooy for insulting Swedish referee Anders Frisk after the final whistle of the Euro 2004 semi-final against Portugal.

UEFA's disciplinary committee will deal with the matter on Friday, European soccer's governing body said on Thursday. The Dutch lost the game 2-1.

The two men were reported to have had a heated argument in the tunnel after the game.

The Dutchman told reporters he believed Frisk had favoured the tournament hosts.

"It's unbelievable how the referee ruled everything in favour of Portugal. He was a real home whistler," Van Nistelrooy said.

"Every 50-50 situation was for them but we cannot do anything about it."