Tottenham's investigation into the apparent racial abuse of Chelsea defender Antonio Rudiger has so far proved "inconclusive", but a Blues fan has been arrested for allegedly abusing Son Heung-min.
Germany defender Rudiger reported being the subject of monkey chants during the match against Spurs, the latest in a series of incidents at all levels of the game this season, and has led to the Professional Footballers' Association calling for a government-led inquiry.
Downing Street said that there remains work to be done by the football authorities to stamp out racism, but did not rule out "taking further steps if required".
Spurs launched an investigation in the aftermath of Sunday's 2-0 defeat but, in an update on Monday, said there has been little progress despite working with lip-readers and having reviewed hours of CCTV footage.
A club statement read: "We are able to track every fan via the cameras and have spent many hours reviewing CCTV footage.
"We have engaged lip-readers to study the footage and contacted Chelsea for further information from their players.
"We have also taken statements from other parties present at the time. The police will be reviewing our evidence alongside us. Please be assured we shall be exhaustively investigating this matter."
The statement continued: "At this time, however, we should point out that our findings are inconclusive and would ask that comment is reserved until the facts are established."
As well as investigating the alleged racist chanting from Tottenham supporters, the Metropolitan Police confirmed a Chelsea fan was ejected from the ground and arrested after committing a racially aggravated public order offence against Spurs forward Son.
A spokesman for the Metropolitan Police said: "Police were made aware of alleged racist chanting during the second half of the Tottenham Hotspur vs Chelsea match on Sunday, 22 December.
"Officers will work with the club in an attempt to identify any people responsible."
The Metropolitan Police have made a total of six arrests as part of the matchday policing operation but none were directly linked to the incident involving Rudiger.
Anthony Taylor, the referee, stopped play after Rudiger claimed he had heard racist abuse and three announcements were made over the public address system at the Tottenham Hotspur Stadium.
Spurs, though, have called for greater clarity on the Premier League's anti-racism protocol.
The club statement added: "In respect of protocols – when the incident was conveyed to the referee Anthony Taylor, he took the decision to call for the implementation of Stage 1 of the UEFA protocol – rather than the Premier League protocol – and asked for an announcement to be made, as well as requesting a further announcement which created a misconception that any issue was ongoing.
The PFA calls for a government enquiry into racism and the rise in hate crime within football and immediate and urgent action from an All-Party Group at the Department of Culture, Media and Sport to address this urgent issue.
— Professional Footballers' Association (@PFA) December 22, 2019
"The Premier League protocol differs from UEFA protocol in that it does not call for an announcement rather that the individual(s) be dealt with by the safety team in the first instance.
"We have asked that the Premier League clarifies the position regarding the use of these protocols to all stakeholders going forward."
The PFA's equalities officer Iffy Onuora insists it is now time for the "warm words" to stop and firm action to start.
He has called for a government inquiry into racism in the game and the need for tougher criminal penalties for hate crime, citing the tough sentences handed down after the London riots in 2011 as a precedent for how a message could be sent out.
Ministry of Justice figures published in 2012 showed that a total of 1,292 offenders were jailed for their part in the trouble with an average custodial sentence of 16.8 months – more than four times the average term handed down by magistrates' courts for similar offences.
"I've seen decisions made on public policy, when they had the London riots and people were getting sentenced to 10 years and things like that, it was a policy decision to send a clear message," Onuora told the PA news agency.
"Well is that only relevant in those particular circumstances? If you threw a five-year jail sentence at someone like this, that's a deterrent right there.
"That's a strong message that you're not tolerating it, rather than warm words after the event."
Damian Collins, the MP for Folkestone and Hythe and who will stand for re-election as chair of the Digital Culture Media and Sport committee, wrote on Twitter: "Racist abuse must be driven out of football stadiums.
"A review on how we can do more to achieve this should also include stopping homophobic abuse and requiring social media companies to do more to prevent abusive attacks against players on their platforms."
— Damian Collins (@DamianCollins) December 23, 2019
Sports minister Nigel Adams called for racist behaviour to be confronted and said: "We will monitor how these plans are implemented before deciding on any further action in future."
The Football Association released a statement saying it was working with match officials, the clubs and the relevant authorities to establish the facts and take the appropriate steps.
Tottenham manager Jose Mourinho, meanwhile, said that there was a wider issue of racism in British society that had to be addressed.
"Society needs help," he said at a press conference on Monday afternoon. "Football is a micro-society.
"We need to eradicate any form of discrimination and in this case we are talking about racism. Football and society needs help."