The Hoops are currently rebuilding under new boss Ange Postecoglou, under whom they have made no fewer than 12 new signings in the recently concluded transfer window.
However, Celtic have had a mixed bag of results across all competitions so far this season, falling to a 1-0 defeat to Livingston in the Scottish Premiership on Sunday in their latest outing.
Celtic also saw some high-profile departures this summer in the likes of Odsonne Edouard, Kristoffer Ajer and Ryan Christie, and Hartson is of the view that Postecoglou needs to bring in more new players when the winter transfer window opens in January as they need more quality in their ranks.
The ex-Hoops star stressed that with all the new additions, Celtic still need more time to properly gel together as team under their new boss.
“I think it [get used to playing together] is going to take them [Celtic] still a bit of time”, Hartson told Sky Sports News.
“The January window, I think Celtic will need to add a few more [players].
“Let us not forget as well, we sold our most potent striker, we sold our best defender.
“We have got new signings that have come in but I think it takes a bit of time to gel.
“The new manager, when you think, he has to build a whole new team.
“That is going to take a little bit of time for them all to gel and get used to playing with each other.”
It remains to be seen how Celtic will approach the next transfer window, when Postecoglou will have a better idea of where his squad are in terms of their quality.
