Livingston raised more questions defensively as they inflicted a fifth away defeat of the season in Sunday’s SPFL Premiership encounter, which left Celtic sixth in the table.
Hartson believes his former team needs to toughen up and employ a mentality similar to his team-mates during his own Parkhead playing days – but is confident the team will begin to learn from the past. “There was myself, [Chris] Sutton, Bobo [Balde], [Stanislav] Varga, Johan [Mjallby] and Henrik [Larsson] was tough. We had some big lads in there,” Hartson recalled.
“I remember talking to Alex McLeish a few years ago and he said he was having kittens every time they conceded a corner to us lot!
“But there was also a mentality. You need that will to say, ‘I’m going to win that ball, going to earn the right to play’.
“This is a young Celtic side. It will come.”
Despite a third defeat in the league Celtic still boast a 12-goal advantage after just six games, a clear indicator of where the weakness lies.
Hartson added: “Ange wants to attack, he wants to outscore the opposition, but he’ll also know we need to improve defensively.
“The manager has come in at a difficult time and there was always going to be a transition.
“He’s brought in exciting players like Kyogo [Furuhashi] and [Liel] Abada and it’s still really early.
“Once Celtic strengthen defensively and get a few players back, I am sure results will improve.”