"I'M on the Deila bus now." Mercifully, John Hartson has not succumbed to further poor health or fallen on hard times.

Instead he has been happily gorging of late on piece after piece of humble pie.

The former striker was until recently part of a lengthy list of ex-players, pundits and supporters casting doubts over Ronny Deila's suitability as Celtic manager. The Norwegian's inexperience, combined with the failure to qualify for the Champions League as well as a smattering of poor league results, had led to some fairly public criticism coming his way. It has not all abated now but the din has grown noticeably quieter.

Sunday's 4-0 thrashing of Aberdeen has all but ensured Celtic of a fourth successive league title. They will contest the League Cup final against Dundee United a week on Sunday, and face the same opposition in the William Hill Scottish Cup quarter-finals this weekend. A treble in his maiden season is certainly within Deila's grasp. Even then there will be some who insist he should have won it all more convincingly given the poverty of the opposition but Hartson, as he launched his foundation's charity golf day, was man enough to admit he had been won over.

"I've jumped on the Ronny Deila bus," he confirmed. "I think myself, the supporters and lot of the media were all critical. I wasn't alone. The European results, and the fact they got a reprieve and still lost to Maribor, meant everybody was on his back.

"But all of a sudden now he's in the ascendency, winning games and has turned things around. And for me we all have to hold our hands up and say "fair play".

"I'm man enough to do that because there's no getting away from the fact he's doing well now. He's come through the spell where he was getting criticism. The crowd idolise him now and love all the fist-pumping celebrations.

"So I've got to be prepared to stick my neck out again and say he's doing a very good job. I'm pleased about that too, by the way. Initially my opinion was different but no-one can tell me they didn't criticise him or they were totally sure about him.

"I'd reckon the Celtic board were asking questions after the first four or five games. Let's not get away from that. That was my opinion too. But I reached a stage where I had to recognise the fact he'd turned it around. I'm with the crowd and I'm with him, I want him to do well.

"I scored 110 goals for Celtic, I have a Celtic tattoo on my arm, I'm a Celtic person and I want the team to do well. I don't want to criticise all the time. But I couldn't say they were playing well when they weren't."

Deila is just 39 years old and managing overseas for the first time in his career. It would have been the easiest thing had he sought out a Plan B during the difficult early months, or ditched his principles for a more pragmatic approach. Instead he has stuck steadfastly to his guns and been rewarded for it. Hartson is impressed.

"Every question we've thrown at him he's answered," added the Welshman. "He's brought in some good players, has got the best out of his skipper, Scott Brown, and things are looking good. Look at Kris Commons who was a shoe-in just a couple of weeks ago and yet the two new signings have been different class. Gary Mackay-Steven and Stuart Armstrong are good players and so is Stefan Johansen who scored again at the weekend.

"I just think they look very, very strong domestically and should take a lot of positives from the two games against Inter Milan. They'd only lost two goals before coming to Celtic Park and ended up letting in three that night. So Celtic showed they can score goals so credit to Ronny.

"As I said, I was critical but so was everyone else. Let's not forget that. But I'm pleased because I want them to win the treble and achieve good things. As yet they've won nothing yet but it's looking good for them."

Celtic will move nine points clear at the top with victory over St Johnstone tomorrow but Hartson was never convinced there was a genuine title challenge to begin with.

"I never thought Aberdeen would win the league and I don't say that disrespectfully," he added "Even if they had won on Sunday I think they might have slipped up over the last nine or ten games."

- John Hartson was helping launch his foundation's golf day that takes place at Mar Hall on Tuesday, April 21. For more information visit www.johnhartsonfoundation.co.uk