Leif Sundell and his two appointed assistants for the Cup-Winners Cup first leg tie in Seville next Thursday are said to have watched the game from the Betis directors' box.
And that is against Uefa's policy that clubs should have no contact with any officials appointed to their European games until the day before the match - a policy designed to eliminate any possibility or suggestion of bribery.
A Chelsea spokesperson said today: "We have asked Uefa to look into the matter."
A Uefa spokeswoman said: "We shall try to find out about this and if it is correct we will first of all ask Real Betis for an explanation."
In fact, the Spanish club - who will come to Stamford Bridge for the second leg of the tie on March 19 - could face a heavy sanction even if Sundell's appearance at the Espanol game was entirely innocent.
And the Blues may even ask for a new set of officials to be appointed for both legs to make sure there is no suspicion of irregularity.
Television footage taken by Canal Plus shows Sundell and several other Swedish officials chatting to Betis fans during Sunday's match."[Sundell] was recognised by some fans and had to put up with their jokes about the result of the forthcoming game," said the Spanish sports daily Marca yesterday.Reuse content