There are now "question marks" over whether Neil Lennon should be appointed Celtic manager permanently, says ex-Parkhead striker Scott McDonald.
Lennon has won six of his nine games in charge since replacing Brendan Rodgers in February.
However, Sunday's 0-0 draw with Hibernian at Easter Road was the third time his side have dropped points.
"It's not been as sharp, as quick; they've just been managing to do enough to get through games," said McDonald.
Lennon won three league titles and two Scottish Cups in his first spell in charge of Celtic.
And the champions are closing in on an eighth title in a row, with a Scottish Cup final place also secured as they bid to win a treble treble.
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But the Celtic board has yet to announce whether Lennon will be given the job beyond the summer, with the 47-year-old having left Hibs in January when the Easter Road side were eighth in the Scottish Premiership.
"When they came back from the winter break they had all guns blazing, they were playing some fantastic football," McDonald told BBC Sportsound. "Since then it's just been a little lull.
"The players believed in Brendan Rodgers: in his shape, in his system. They kept believing they were going to get better. So for someone now to come in and tell them different it's going to be very difficult.
"The Celtic fans will be thinking right now, 'we went and spent £3m on a manager previous to now' [when Rodgers arrived in 2016]. They do not want to go backwards on that. They want that £3m spent once again to get a top quality manager.
"I know for a fact that everything Brendan has done, everything he's worked on, even the grassroots at the club - that will not change. That is there to stay, that philosophy is going nowhere."
Lennon 'has kept Celtic going'
Former Celtic goalkeeper Pat Bonner says Lennon has "kept them going" as he steers them towards the Premiership title.
"He's filled in a gap, he's done okay, and he's kept them going," said Bonner.
"But you can't bring a manager in and tell them, 'you have to play the same way Brendan Rodgers did'. You have to find someone who is close to Brendan Rodgers or you've got to then change it."