Chelsea boss Jose Mourinho claims he saw Barcelona coach Frank Rijkaard enter referee Anders Frisk's dressing room during half-time at the Nou Camp.
And the Blues chief executive Peter Kenyon has said the club will report their concerns to Uefa.
"We as a club are putting in a report," Kenyon told BBC Five Live's Sportsweek.
"There was an incident at half-time which we weren't happy with. It was a real situation and we're making a point, not an official complaint."
Mourinho refused to speak after his side's 2-1 defeat in the Champions League first-leg encounter.
But the Blues boss has told Portuguese newspaper Dez Record: "When I saw Rijkaard entering the referee's dressing room I couldn't believe it.
"When Didier Drogba was sent off (after half-time) I wasn't surprised."
Kenyon supported Mourinho and insisted his manager's post-match silence was not an "over-reaction".
"To react the way Chelsea have is pathetic"
"We don't think it was necessary to make an official complaint, but we do think we need to bring the attention to something we weren't happy with regarding the referee at half time.
"That report will be going into Uefa this week and I know Uefa will treat it seriously and give it the due attention it requires."
Mourinho has also claimed that Pierluigi Collina is likely to referee the second leg.
"There is something that tells me that in London the referee will be Collina, the best in the world," said Mourinho.
"A perfect referee with personality and quality."
But Uefa spokesman William Gaillard told the Sunday Telegraph: "We have made no decision at all on this."
"Chelsea are inventing something that didn't happen"
Gaillard also confirmed that Uefa has asked Chelsea to explain why Mourinho and his players refused to speak to the press after the game and why they were late in appearing for the second half.
"One is a violation of the competition, the other of the rules of the game," he said.
"They will be dealt with by our control and disciplinary body, probably resulting in a fine depending on the evidence we receive."
Barcelona assistant coach Henk Ten Cate has branded Chelsea's threatened complaint to Uefa as "pathetic".
"To react the way Chelsea have is pathetic. Mourinho lied with the line-ups, and now this," Ten Cate said.
Rijkaard was critical of Mourinho's decision not to speak to the media after the match.
"There was a lot of talking before the game and now surprisingly there is a lot of talking after the game. It is not good behaviour after a match," he said.
"Maybe they want to start something and make it worse than than it is. I really don't understand it. I am calm about it."