The Blues contacted the police over two "totally unacceptable, disgusting and abhorrent" posts directed at Nigeria star Mikel following Wednesday's Champions League draw with Juventus on Thursday night.
The abuse occurred at around the same time Mikel deleted his Twitter account, although Chelsea insisted the 25-year-old had not been aware of it and had been intending to leave the social media site in any event.
Manager Di Matteo said today: "His intention was to close the account anyway. So it was a good reason to close it.
"The social media world, especially Twitter - because it's anonymous and so on - it's a dangerous vehicle to express yourself.
"I don't think it's fair. If somebody has to express his opinion, he should put his face to it."
The abuse of Mikel occurred after his mistake helped Juve come back from 2-0 down in Wednesday night's Group E game, something for which the midfielder immediately apologised.
News of the tweets about him emerged on the same night Lazio fans were accused of directing monkey chants at Tottenham's black players in the sides' Europa League clash at White Hart Lane.
Di Matteo added: "There's a lot of campaigns against (racism) and we have to try our best to fight it in every possible way.
"We should try to make the people understand that it hurts other people, chanting and things like that."
Chelsea were keen to stress on Friday there was no currently no evidence that the racist abuse of Mikel had come from their own supporters.
But they promised lifetime bans for those involved if that proved to be the case.