Ajer’s form has stood out despite Celtic’s struggles and he has looked much sturdier at the back despite the rest of the defence around him failing.
The Norwegian has been linked with a move away from Celtic and there are suggestions he is on the radar of Serie A giants AC Milan for a potential move in the summer.
But Hartson feels Ajer has been the leader on the pitch for Celtic and his performances at the back are instrumental in Celtic getting even draws in recent games.
The former Bhoy believes the defender has shown commitment and gumption with his performances and is of the view the Celtic players should follow his example on the pitch and had they done so then the side would be in a much better spot.
Hartson said on the Ten10 Celtic Podcast: “If you were going to pick a captain you’d have to give it to Ajer at the minute because he is instrumental the way that he’s playing.
“He’s grabbing the bull by the horns and he’s almost dragging the team through, even to these draws.
“You see him making these lung-bursting runs forward, he’s marauding with that big stride, he’s challenging, on his backside, making blocks, in the opposition’s penalty area.
“He’s right-back, centre-half, he never moans, he just gets on with it.
“He’s a credit to the rest of the players.
“They should all look at him and if they’d all adopted the same attitude as Ajer then might have made a better fist of it in terms of holding on to the title.”
Ajer’s form aside, Celtic are struggling and they are on a four-game winless streak in the league, their worst such run in 21 years.