As a player, Lennon joined Celtic in 2000 and won five titles in seven seasons, and reached the UEFA Cup final in 2003.
He left the club in 2007 to join Nottingham Forest but returned to Celtic Park a year later as a member of the coaching staff.
Lennon's reign was not without controversy as he received a four-match touchline ban following a spat with then Rangers assistant manager Ally McCoist in March 2011. In other incidents the same year, a letter bomb addressed to the Celtic manager was intercepted by Royal Mail staff in 2011 and Lennon was attacked by a Hearts supporter.
Former Celtic player Henrik Larsson, currently in charge of Swedish club Falkenbergs, is favored to succeed Lennon.