Kilmarnock have condemned racist abuse directed at manager Alex Dyer and are working with Police Scotland to identify the individuals involved.
The Scottish Premiership club received a letter on Saturday morning following the 2-1 home defeat to Livingston on Boxing Day.
"Kilmarnock Football Club utterly condemns a letter which was delivered to the club this morning containing racist abuse directed at our manager, Alex Dyer," read a club statement on Monday evening.
"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."
Livingston's late winner on Saturday made it five defeats in a row for Kilmarnock and eight losses in nine league games.
Dyer responded to the defeat by saying he would have no complaints if the Rugby Park board decided his time was up, although he believes he retains its backing, as well as that of his players.
Eighth-placed Kilmarnock's next game on Wednesday is away to Motherwell, who are below them in table on goal difference.
