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 English Premier League match against Spurs, the latest in a series of incidents at all levels of the game this season.
It led to England's Professional Footballers' Association calling for a government-led inquiry.
The British prime minister's office said 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 had been little progress despite working with lip-readers and having reviewed hours of CCTV footage.
"We are able to track every fan via the cameras and have spent many hours reviewing CCTV footage," the club said in a statement.
"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.
"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, police confirmed a Chelsea fan was ejected from the ground and arrested after committing a racially aggravated public order offence against Spurs forward Son.
Police made a total of six arrests as part of the match day policing operation but none were directly linked to the incident involving Rudiger.
Tottenham manager Jose Mourinho said 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."
Australian Associated Press