West Ham United midfielder Edson Alvarez reportedly threatened to kill Chelsea's Enzo Fernandez during Saturday's London derby.
Chelsea won the game 3-0 with all of the goals coming before the 48th minute.
Seemingly angry with the way the game was going, Alvarez fouled Cole Palmer shortly after the Englishman had scored Chelsea's third goal.
The Mexican was shown a yellow card by referee Samuel Barrott but the drama did not end there.
Moments later, Alvarez was seen shouting something at Argentina international Fernandez while secretively covering his mouth.
Alvarez shouted at Enzo Fernandez, who responded by calmly patting him on the back
However, despite Alvarez covering his mouth, some of his words were picked up by the pitchside microphones.
According to Argentine daily newspaper OLE, Alvarez told Fernandez: 'I'll wait for you... I'll kill you outside, wherever you want.'
Fernandez did not appear overly worried by this alleged threat and he defiantly responded by patting Alvarez on the back and telling him: 'Go ahead'.
Perhaps sensing that he was at risk of losing his cool and being shown a red card, Hammers manager Julen Lopetegui subbed Alvarez off five minutes after his booking.
Fernandez stayed on the field until the 84th minute when he was replaced by Kiernan Dewsbury-Hall.
Chelsea have now won their first three away games in the Premier League this season, having already beaten Wolves and Bournemouth on the road.
Saturday's win took Chelsea up to fourth place in the table.