The Sun says hundreds of supporters repeatedly sang 'Anton Ferdinand, you know what you are.' UEFA are unlikely to take disciplinary action - the ref did not mention it in his report - but the Blues are ready to ban any culprits identified by TV footage.
A club spokesman said: "The chanting by a vocal minority was wholly inappropriate.
'We will be working with the authorities to seek out those responsible. Chelsea FC believes - as we are sure do the vast majority of our fans - that all forms of discrimination are abhorrent and have no place in our society."
But many others took to the internet to condemn the reaction.