CELTIC manager Neil Lennon was left shocked by the racist abuse directed at Kilmarnock manager Alex Dyer in a letter.
Killie are working with Police Scotland to identify any individuals involved in sending the letter to the Rugby Park club following the 2-1 home defeat to Livingston on Boxing Day.
The Ayrshire club condemned the "disgusting act" and Celtic boss Lennon was supportive of Dyer.
He said: "Alex is one of the best football men I know up here.
"I think it's shocking in this day and age that a guy of his calibre and standing has to put up with any sort of racism at all.
"I know him personally, he is one of the best. I want him to succeed at Kilmarnock as much as anybody else.
"I think he is a great football guy and I think he is good for the game here. We want this eradicated.
"Kilmarnock have come out and supported him very strongly, which is brilliant to see, and he has our full support from everyone at Celtic."
Police Scotland are looking into the letter, which was delivered to Rugby Park on Monday.
Chief Inspector Nathan Calderwood said: "We have been made aware of an offensive communication and enquiries into the matter are ongoing."
Meanwhile, Celtic boss Lennon described the late former Dundee United boss Jim McLean as a football giant as Celtic prepared to host the Tannadice side on Wednesday.
The Tayside club are in mourning following the death of their title-winning boss on Boxing Day at the age of 83.
McLean, who spent 22 years as United manager from 1971, led the Terrors to their only league championship in 1983, and made them a force in Europe, reaching the European Cup semi-finals in 1984 and the UEFA Cup final in 1987, beating Barcelona at home and away on their way to the latter.
Hoops boss Lennon said: "I grew up in that era, 13/14 and you had the New Firm of Aberdeen and Dundee United as well as Celtic and Rangers and he was a giant.
"His Dundee United team was one of the best put together in any generation of Scottish football.
"I remember them beating Barcelona and I remember also being really disappointed that they lost the UEFA Cup final to Gothenburg.
"But an incredible achievement and they won the league. He was a giant, really intelligent, a great football guy.
"I got to speak to him a few years ago, I rang him and I think he thought someone was taking the mickey.
"I was at Hibs at the time and I asked him for a little bit of advice but he was a little tentative coming forward because he wasn't sure if it was me or not.
"But a huge loss, particularly to Dundee United because he was the greatest manager they ever had by a country mile and some of the players and teams he produced were out of this world."
After the last game of 2020 against United, Lennon's side will face Rangers at Ibrox on January 2, the 50th anniversary of the Ibrox Disaster.
Following an Old Firm encounter which ended 1-1, 66 fans died and around 200 were injured in a crush on stairway 13.
Lennon said: "My father-in-law was at the game and luckily enough he left early.
"An absolute tragedy. I was at Ibrox a few years ago and it was one of the most poignant moments I have had in my time here when we laid a wreath on the pitch.
"So, it will never be forgotten. We do think about the families who have lost (loved) ones, going to a football match and not coming back, I can't think of anything worse really."
