“I would like to thank so many people at the club who have given me so much and I would also like to thank my family for their love and support. I wish the Celtic supporters, players, staff and directors nothing but success for the future.”
Celtic chief executive Peter Lawwell added: “I would like to pay tribute to Neil for all he has done for the club in his second spell, delivering our eighth and ninth successive league titles, the quadruple treble and winning the last five available domestic trophies.
“Neil has always been and will always be a true Celtic man and someone I will always hold in the highest regard.
“I have watched Neil fight many battles over many years, on and off the field, with a courage and tenacity few could match. Even this season, he has fought so hard and worked tirelessly to turn things around.
“While this season has not progressed as we would have liked, it cannot diminish the character or integrity of a man who has given the club so much.
“Personally, it is a sad day for me to see Neil leave the club. Neil is a man of quality and decency, he is someone who will always be part of the fabric of Celtic and someone who will always be welcomed at Celtic Park.”