Ronny Deila’s men moved six points clear at the top of the Scottish Premiership on Sunday after a 4-0 over Aberdeen and could go even further ahead if they beat St Johnstone on Wednesday.
The Scottish champions are also in the League Cup final and the Scottish Cup quarter-finals – both against Dundee United.
“Even if Aberdeen had won on Sunday they might have slipped up over the last nine or 10 games.
“Celtic can go nine points clear on Wednesday if they beat St Johnstone and they look unbeatable domestically. They have brought in the two lads from Dundee United and they’ve given the group a lift.
“I’m not being disrespectful to the other clubs but the Treble looks a real possibility. There is a League Cup Final to look forward to, the league looks a shoo-in now.
“Apart from an absolute calamity or switching off and being naive I can’t see past Celtic.”
Hartson also admitted he got it wrong about Deila.
“I’ve jumped on the Deila bus now. 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 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 very well now.”