Celtic chairman Peter Lawwell has confirmed he will step down from the club's board at the end of December, citing "intolerable" abuse as the reasoning behind his decision. 

Lawwell joined the club in 2003 as chief executive, holding that position for 18 years, before returning to Celtic Park two years ago as non-executive chairman.

However, the club's board have been the subject of fan protests this season following several issues on and off the pitch, which started with a lacklustre summer transfer window.

Celtic also failed to qualify for the Champions League proper, while they trail Hearts in the Scottish Premiership table by six points, though they do have two games in hand. 

Brendan Rodgers resigned as head coach in October and Martin O'Neill took temporary charge, which brought an upturn in results, before Wilfried Nancy was appointed earlier this month. 

But Nancy has had a difficult start to his tenure, losing all three of his first matches across all competitions ahead of Wednesday's visit to Dundee United. 

And Lawwell, who oversaw a total of 38 trophy triumphs during his time in Glasgow, says the abuse and threats are now too much to bear. 

"I believe I have shown my ability to overcome challenges on many fronts, but abuse and threats from some sources have increased and are now intolerable," Lawwell said.

"They have dismayed and alarmed my family. At this stage in my life, I don't need this. I cannot accept this, and so I leave the club I have loved all my life.

"The motivations and aims of these detractors can be investigated by others. I prefer to look back on my career at Celtic with deep gratitude and satisfaction."

Principal shareholder Dermot Desmond paid tribute to "all he has given" to Celtic over so many years.

He pointed out that Lawwell had overseen a number of improvements at the club, including the upgrading of Celtic Park and the construction of their training centre. 

"I am personally very sorry to lose Peter, but I understand and respect his decision in light of recent events and what he has endured," Desmond added. 

"As chief executive, Peter was the driving force of the club and, in his later role as chairman, he oversaw board affairs.

"Peter has witnessed 38 cup or title triumphs in his time at the club, a period of extraordinary domestic dominance for us as, and we have also competed in European football."