The Norwegian boss confirmed this week that he will be leaving Parkhead at the end of the season.
Ronny Deila finally put longstanding speculation about his future to rest this week by announcing that he will be leaving the club at the end of the season, and in a frank press conference the Norwegian boss has outlined his key reasons for making the decision, as quoted by the club's official website.
The Bhoys look set to win a fifth league title in a row after Deila won the league and League Cup double in his first season, but this campaign has been far from plain sailing for the club or the manager.
The Hoops were knocked out of the Champions League before even reaching the group stage, and then finished bottom of their Europa League group after failing to win any of their six games.
They lost 3-1 to Ross County in the semi-finals of the League Cup, and Sunday's penalty shootout defeat to arch-rivals Rangers at the same stage of the Scottish Cup proved to be the trigger for the manager to announce his departure.
However, Deila revealed that his decision has not been a knee-jerk reaction and has been made after much contemplation on his part.
He told reporters that the lack of improvement the side have made since his arrival "kills me inside" and said he felt that meant it was time to pass the torch.
Deila said, as quoted by Celtic's official website: "I’ve been thinking about it for little while because I have felt the team hasn’t got the results they should have and, maybe the most important, the performance that I wanted or the improvement.
"When I started and came into this job I talked about improving the team and playing attractive football and in the last six months we haven’t had the improvement that we need. One of the reasons we haven’t had that improvement is because of all the pressure and speculation around me all the time.
"When you don’t get improvement, and it’s one of my biggest values, it kills me inside. I lose energy over that and that’s why you’re a manager, because you want to improve individually and the team. To see the performance now I don’t think there has been a lot of improvement and that’s one of the reasons. Also, when you don’t get improvements, then the outside pressure grows as well.
"Before these last five games I think it’s best for the club and for me that new energy comes into the club after the season. Now we can really focus on winning the five games and getting five in a row. That’s going to be a huge thing for me and also for the players and the whole club. This is why the decision has been made."
Speculation is already rife as to who will replace Deila, with names such as David Moyes and ex-Bhoys boss Neil Lennon thought to be at the forefront of the list.