Chelsea are "totally satisfied" the steward accused of racially abusing Barcelona striker Samuel Eto'o has no case to answer.
The Blues have carried out their own investigation into the incident, alleged to have taken place after the 4-2 win which sent Barca out.
"The steward is extremely upset that this accusation has been levelled against him," a spokesman said.
"The club are totally satisfied that he did not make a racist remark."
The spokesman added: "We completely refute the allegation being made against him."
Chelsea interviewed the steward who Eto'o claimed had made the racist jibe and also took statements from eyewitnesses who were in the players' tunnel at that time.
"Chelsea have an excellent record of supporting anti-racism campaigns both in England and in Europe and the club condemns all forms of racism," the spokesman said.
"We now hope this matter is closed and we can all focus on what was a wonderful match."
Chelsea earlier said the incident, which was not mentioned in referee Pierluigi Collina's report, never took place and their stewards were just trying to "defuse what was becoming a potentially volatile situation."
Club spokesman Simon Greenberg added: "This is extremely serious which is why we've come out with a firm rebuttal."
European governing body Uefa has also admitted it is unlikely to take action.
Uefa's communications director William Gaillard believes little else can be done.
"Unless we have some firm evidence about the alleged racist remark there is little we can do, otherwise it is just one man's word against another," said Gaillard.
"I am not suggesting for a moment he is telling lies - he strikes me as a very honest and charming man - but we would need sound or video evidence, or some independent verification, to take any action."
English football's anti-racist campaign group, Kick It Out, had asked for an investigation into the matter.
"Any complaint of racism has to be taken seriously - people don't generally make these complaints up," said Kick It Out spokesman Piara Powar.
"Although Barcelona lost the game I don't see how it would help Eto'o or Barcelona to make these kind of allegations without foundation. It needs to be investigated."
Barca coach Frank Rijkaard also played down the tunnel fracas after the game.
Rijkaard had to be restrained after the final whistle, but insisted: "It was not a big deal.
"You know what it's like after an emotional game like that, all feelings running high. Someone came forward and kind of insulted us on our bench.
"I don't know who it was, just some guy. It was nothing serious."
Reflecting on the game - and the war of words beforehand - the Dutchman added: "You always feel bitter after a loss, but maybe I feel a bit more bitter because of all the lies that were told before this game.
Barcelona players remonstrate with referee Pierluigi Collina
"I suppose all the stuff surrounding the game wants you to win a bit more, and makes it hurt more when you lose.
"These things happen when people show their emotions sometimes."
Cameroon international Eto'o said that an exchange with an unknown figure had made him "very angry" and he also took a verbal swipe at Mourinho's Chelsea and referee Pierluigi Collina.
"Mourinho is shameless. If this team wins the Champions League, it would make you want to retire," said Eto'o.
"With so much money and so many players, what they do is not football."
"Collina helped Chelsea, he denied me a clear penalty and for the fourth goal they fouled Victor Valdes, but those things happen," he added.
But Chelsea's communications director Greenberg is hoping the ongoing controversy does not overshadow the team's achievement of reaching the quarter-finals.
"The game was played in excellent spirit," Greenberg added.
"Regardless of the incident that happened at the end of the game, I can tell you as I was in the tunnel that players were shaking hands and swapping shirts.
"The incident that occurred didn't involve any of our players and appears to centre around mostly the Barcelona players and our stewards attempting to diffuse what was becoming a potentially volatile situation."
Meanwhile, Uefa has already been asked to investigate claims that Rijkaard met referee Anders Frisk in his dressing room at half-time of the first leg at the Nou Camp.
And the Blues are facing a double disciplinary charge for their late arrival for the second half in that game, and for Mourinho's absence from the post-match news conference.
The draw for the quarter-final will be made on 18 March at Uefa's Swiss headquarters.