Alan Thompson is seeking legal advice after he was sacked from his position as first-team coach at Celtic.
The 38-year-old was given the news in a telephone conversation with manager Neil Lennon on Sunday.
His lawyer, Margaret Gribbon, of Glasgow-based Bridge Litigation, said in a statement: "I can confirm that I have been instructed to act on behalf of Alan Thompson following his dismissal by Celtic FC.
"Alan was informed of the decision to terminate his employment with immediate effect in a telephone conversation with the club manager Neil Lennon."
Celtic confirmed the former Parkhead midfielder had left the club. In a statement, the Scottish champions said Thompson was called by Lennon after he refused to meet the Celtic manager in Newcastle on Sunday.
The statement added: "The matter is now in the hands of lawyers and, therefore, we are unable to go into any further details."
Thompson, who was a long-serving player with the club under Martin O'Neill, had been working as part of the coaching team since June 2010, when along with former team-mate Johan Mjallby, he agreed to work under manager Lennon.
The midfielder played for the Glasgow club between 2000 and 2007, winning four Scottish Premier League titles, three Scottish Cups and two Scottish League Cup medals. Along with Lennon and Mjallby, he was part of the team that reached the Uefa Cup final in 2003.
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