Kilmarnock manager Alex Dyer has been racially abused in a letter sent to Rugby Park.
Police are now investigating the incident that took place on Monday as they look to trace the person responsible.
The Premiership side condemned the letter in a statement released on Twitter which said: “We utterly condemn a letter which was delivered to the club containing racist abuse directed at our manager.
“We are working with Police Scotland to identify any individuals involved in this disgusting act and we will pursue the strongest possible action we can against them.
“Racism in any form is completely unacceptable and must be called out whenever and wherever it is found.
“As a club, we have shown our support to rid the game and society as a whole of racial discrimination by taking the knee before each fixture this season and we will continue to do so.”