Chelsea has asked police to investigate racist abuse directed at midfielder John Obi Mikel, while UEFA opened disciplinary proceedings against Italian club Lazio after black Tottenham Hotspur players were apparently taunted during a Europa League match.
Racist tweets were sent to Mikel after the Nigeria international's mistake in Wednesday's Champions League opener against Juventus led to Chelsea conceding an equalizer.
Chelsea says, "We've informed the police and support taking the strongest possible action."
Mikel deleted his Twitter account Thursday.
Chelsea boss Roberto Di Matteo accused Mikel's Twitter trolls of hiding behind their keyboards as he condemned the racist abuse of the midfielder.
"His intention was to close the account anyway. So it was a good reason to close it," Di Matteo said. "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."
Chelsea stressed that there was no evidence that the racist abuse of Mikel had come from its own supporters but promised lifetime bans for those involved if that proved to be the case.
Tottenham manager Andre Villas-Boas didn't hear the abuse, and says, "It's for the authorities (UEFA) to follow up in any kind of investigation."
UEFA confirmed Friday it had opened disciplinary proceedings against Lazio. After receiving reports from last night's referee Ovidiu Alin Hategan and match delegate Adonis Procopiou, European football's governing body charged the Rome-based club with improper conduct.
UEFA's Control and Disciplinary Body will hear the case Oct. 18.
Also Friday, Bulgarian club Levski Sofia said it has been fined $39,000 by UEFA for racist abuse by their fans at a Europe League match against Bosnian team Sarajevo in July.
On Wednesday, British lawmakers urged soccer authorities to do more to combat racism in the game.
Article 11 of UEFA's disciplinary regulations states that Lazio can expect a fine of $26,000 if their fans are found guilty of racial abuse.
Should it decide further action is deserved, UEFA could force Lazio to play one or more of their games behind closed doors.
They could even be stripped of some of their points or disqualified from the competition altogether, although this punishment is likely to be meted out in only the most extreme cases.
Last season, UEFA fined Porto $27,000 for its fans' racist abuse at Mario Balotelli and Yaya Toure, but then caused outrage by fining Manchester City $40,000 for being one minute late back on to the pitch after half-time during the Europa League clash.
Piara Powar, executive director of anti-discrimination Football Against Racism in Europe (FARE), thinks UEFA should force Lazio, whose "Ultra" supporters are synonymous with the far right, to play their next game behind closed doors if found guilty.
"UEFA normally operate a 'three strikes and you're out' policy, and I think Lazio are at first base in that respect, but if (UEFA) really want to set the bar high, if they really want to send out a strong message, then I think they can do so regardless of whether it's a first or second offense," he said. "I therefore think that UEFA could move directly to something like a match behind closed doors (punishment). They could suspend that punishment, perhaps, and then if something happens further down the line, then they can trigger that.
"Lazio are a strong club. They have been part of the European football scene for a long time. There needs to be quite a hard symbolic action taken when these instances occur. This punishment is one way of waking the club and the fans up to some of the problems that they face."
The London Metropolitan Police confirmed that no complaints about alleged racist shouting had been made, while the managers of both teams involved said they did not hear anything untoward.
Tottenham has not made a formal complaint to UEFA and is happy for the governing body to take care of the matter as they see fit.
Friday, Barclays Premier League managers united in urging UEFA to take a hardline stance on racism.
Arsenal boss Arsene Wenger said: "How we improve things is by being absolutely resilient to fight against stupidity. It looks like it will be an endless fight but we have to fight against it, against stupid reactions from the crowd and I'm certain we have to be tougher at every level."
Aston Villa manager Paul Lambert said: "It's not right. There's no place for it in any walk of life, let alone football. Hopefully UEFA can do something about it. You'll still get a minority of idiots out there who do it, but there's no place for it."
Information from The Associated Press and Press Association was used in this report.