Chelsea's 2-0 Premier League win over Tottenham Hotspur was overshadowed by allegations of abuse hurled at Antonio Rudiger on Sunday.
The German defender was involved in an incident that saw Tottenham's Son Heung-min red-carded just past the hour mark and shortly afterwards indicated that he had been the victim of a monkey gesture from the home section.
Several announcements were made over Tottenham's public address system saying "racist behaviour from spectators is interfering with the game" while referee Anthony Taylor stopped the game to talk to the players.
"My understanding is that there was a racist comment or gesture. I know Antonio reported it to (captain) Cesar (Azpilicueta) out on the pitch," Chelsea manager Frank Lampard said. "They are now talking to the officials and going through the right procedure. No matter what stadium it is in, we do not want that in the game."
Lampard played down a suggestion that his players could have walked off, saying the facts needed to be established first.
UEFA's three-step protocol states that a game can be abandoned if fans have been warned twice before.
"We are now conducting a thorough investigation, which will include liaising with Chelsea and their players for their observations. Any form of racism is completely unacceptable and will not be tolerated in our stadium," Tottenham said in a statement.
"We take any such allegations extremely seriously and shall take the strongest possible action against any individual found to be behaving in such a way, including stadium bans."
Azpilicueta said the incident happened after the red card to Son, after he kicked out at Rudiger following a tussle.
"Toni came to me and said he was listening in the crowd monkey noises," the Spaniard said. "I reported it to the referee. We have to work together to eradicate the problem. It is an issue in life and football.
"It is made very clear to us all that if we have heard any racist incident to report it. Altogether we need to make it stop. I hope everything gets clear and we eradicate it as soon as possible."
The alleged racist incident is the latest one at a high-level Premier League game. Manchester United's Fred claimed he was victim of a monkey gesture by a Manchester City fan.
In July Chelsea banned one of their fans for life after he racially abused Manchester City's Raheem Sterling.
Tottenham defender Toby Alderweireld said players were "sick of it" when asked about the incident while Tottenham manager Jose Mourinho said "every club was together" in the battle to eradicate racist behaviour from the stands.
"I was losing, I didn't want the game stopped but immediately when I knew the reason why it was stopped I obviously understood and accepted it," he said.
"The club is also a very proud club in this kind of situation and the club also internally will try to delete it.
"I'm disappointed that things like that still can happen, but the referee stopped the game. He spoke to the players, he spoke to the captains, he spoke with the coaches."