UEFA will investigate allegations that Liverpool striker El-Hadji Diouf spat at Celtic fans during last night’s UEFA Cup quarter-final.

They are awaiting official reports on the incident, and will examine video evidence before deciding whether to take any action. Strathclyde police have also questioned the Senegalese player and have passed the allegation to the Glasgow Prosecutors office.

As well as internal action being taken by Liverpool, Diouf may find himself facing legal prosecution and receiving a ban from UEFA. He will know his fate before the return leg next week.

Manager Gerard Houllier said: “It was the shame that the incident cast a shadow over the performance of my team.

“The player has apologised for his reaction. It was totally inappropriate whatever the provocation … Liverpool do not condone this act in any way and will deal with it internally.”

On the pitch, the all-British affair ended 1-1. Celtic started superbly and were a goal up after 105 seconds. Henrik Larsson, starting his first game for a month, bundled the ball in from close range.

After a torrid opening 10 minutes Liverpool began to get back into the game and Emile Heskey equalised after 17 minutes.

Elsewhere, Simone Inzaghi came off the bench to score the only goal of the game to give Lazio victory over Besiktas.

Coach Roberto Mancini said: “It was a step forward for us today because we scored a goal, even though we created a lot more chances.”

Both Portuguese teams lost 1-0. Porto going down at home to Panathinaikos, when Emmanuel Olisadebe scored with just 17 minutes remaining.

Boavista were beaten in Malaga, with Julio Del Valdes scoring for the Spaniards.

Malaga coach, Joaquin Peiro said: “We are in a good position. Not conceding any goals was very important.”