Chelsea say one of their players was racially abused by Dynamo Kiev supporters during their Europa League game in Ukraine.
Maurizio Sarri's side won 5-0 in last week's second leg to progress to the quarter-finals of the competition, where they will face Slavia Prague.
Olivier Giroud scored a hat-trick with Marcos Alonso and teenage winger Callum Hudson-Odoi also on the scoresheet for the Blues.
But on Monday, Chelsea revealed the club made a complaint to UEFA over racist abuse during the closing stages of the game.
"We can confirm a report of racist abuse directed at one of our players in the final minutes of the match in Kiev from a small section of home supporters," said Chelsea's statement.
"We wholeheartedly condemn such abhorrent behaviour.
"The matter was reported to the referee at the final whistle and the chairman and club secretary spoke to the UEFA match delegate immediately after the match.
"We expect UEFA to conduct a fulsome investigation and we will provide full cooperation."
In November 2015, Dynamo Kiev were ordered to play two European home games behind closed doors after a reported attack on black fans at a Champions League game against Chelsea.
