John Hartson admits he has been completely won over by Celtic manager Ronny Deila.
Welshman Hartson, who spent five years at Celtic between 2001-2006, was critical of Deila as he struggled in his first few months in charge.
But Celtic's recent run of excellent form has left Hartson convinced about the Norwegian manager.
"I'm sensible and wise enough to see he has turned it around - I'm on the Ronny Deila bus," the 39-year-old said.
After watching Celtic go out of the Champions League twice this season, Hartson had claimed Deila, who was named manager in the summer, "did not have a clue".
The Scottish champions have, however, put their early-season problems behind them and they moved six points clear at the top of the Premiership thanks to Sunday's 4-0 win over second-placed Aberdeen.
Celtic are also in the final of the League Cup and they remain in the Scottish Cup as well.
"At the start of the season there was a few of us, myself included, who were quite critical of Ronny," Hartson added.
"I wasn't alone in that. The fans were having a go, so was the media and I'm sure the board was asking questions too.
"There was lots to be concerned about. They lost 6-1 to Legia Warsaw over two legs in the Champions League but got a reprieve, then lost again to Maribor. There was also the defeat at home to Hamilton in October.
"So I was only speaking about what I was seeing at that time.
"He has brought in fresh legs and impetus with the signings of Stuart Armstrong and Gary Mackay-Steven. Defensively, they look very strong with Jason Denayer and Virgil van Dijk in the middle.
"He's got plenty of options up front and they look a really good outfit now. You would be a brave man now to bet against them winning the treble."
Hartson also reckons Celtic's hammering of Aberdeen proves just how far Deila's side have come since the start of the season.
"They are steamrollering teams now," he added. "It [Aberdeen game] reminded me a bit of the Celtic team I played in. If Henrik Larsson, Chris Sutton or myself didn't score, Stilian Petrov or Alan Thompson would.
"And if they didn't, we'd have Bobo Balde, Stan Varga and Johan Mjallby throwing themselves at corners and eventually we would steam-roll sides.
"That's credit to Ronny. When I criticised him, it was nothing personal. I scored 110 goals for this club. I've got a Celtic tattoo on my arm. I want Celtic to do well.
"But people have to appreciate at the start of the season the performances weren't good enough."