Rangers stopped Celtic from winning a tenth league title in a row this season and are 23 points ahead of the Bhoys in the league table with two games left in the campaign.
The Gers have already secured the signing of Zambian forward Fashion Sakala on a free transfer and Steven Gerrard is looking to add more quality over the course of the summer, with the carrot of Champions League football.
Hartson, a former Celtic striker, conceded that he is worried about Rangers next season because of the momentum they are likely to have at the start of the 2021/22 campaign.
He stressed the importance of Rangers resoundingly ending Celtic’s hopes this season and conceded that the Bhoys have an uphill task ahead of them in terms of bridging the gap with Steven Gerrard’s side.
Hartson said on Go Radio Football Show: “That’s what I am worried about, Rangers with momentum.
“The way they have won, they absolutely cantered to a league title in such a huge and unprecedented opportunity for Celtic.
“And the way Rangers responded, some of the football they played have been excellent and it worries me.
“It worries me because Celtic have so much to do to get back to where they were this time sort of 18 months ago.”
Celtic are yet to confirm the appointment of a new manager and a director of football ahead of a summer of upheaval.
