Chelsea have condemned chants by their own supporters about QPR defender Anton Ferdinand during Tuesday's 1-1 Champions League draw at Genk.
The travelling fans repeatedly sang about Ferdinand, who it is alleged was racially abused by Blues captain John Terry at Loftus Road on 23 October.
A Chelsea spokesman said in a statement: "The chanting was wholly inappropriate and we don't condone it."
Manager Andre Villas-Boas insisted he had not heard the chanting.
"I was concentrating on the game," he said.
This incident comes on the day the Metropolitan Police launched a formal investigation into allegations Terry used a racial slur towards Ferdinand during his side's 1-0 defeat by QPR.
It is unclear whether Chelsea could face any action over the chanting.
Terry was an unused substitute at the Cristal Arena as his side squandered the chance to close in on qualification for the Champions League knockout phase.
Ramires put Chelsea ahead but David Luiz saw a penalty saved and Jelle Vossen equalised with Genk's first goal in this season's competition.
Commenting on the performance, Villas-Boas said his side lacked ruthlessness in front of goal.
"We were quite organised in the first half and, in the second half, you are confusing losing control of the game with the emotions coming from the stadium," he said.
"But we created enough opportunities to win the game. It's just not happening for us in terms of efficiency.
"We hit the post, missed a penalty, had chances in front of the posts. It seems we need to focus, in terms of efficiency.
"At 1-0, the game is always close. They created a few chances and one went into the net to make it 1-1.
"It's not a bad result away from home but it's a game we expected to win. We have to react."
The Blues are top of Group E on eight points, two clear of Bayer Leverkusen on six and three in front of Valencia on five.
They club go to Leverkusen on 23 November and finish at home to Valencia on 6 December.
"It gets a little bit tighter," said Villas-Boas. "We go away and it's a bit tighter but we have responsibilities that we don't escape.
"Our job is to qualify first and that's what we would like to do."
Chelsea were hoping to return to winning ways after back-to-back Premier League defeats by QPR and Arsenal.
