The former Hoops striker feels the club still have some work to do.
John Hartson - Celtic celebrates
John Hartson has taken to social media to share his thoughts on what Celtic need to do to improve their odds of qualifying for the Champions League.
The Hoops narrowly scraped past FK Astana last night, courtesy of two penalties in stoppage time in both halves, to progress into the play-off qualifying round.
Celtic's Moussa Dembele in action with Lincoln's Bernardo Lopes
A tricky tie awaits Brendan Rodgers’ men and Hartson took to Twitter to comment on what the club needs to do next:
They must.. 3 quality signings I would like to see happen. Kick on ! https://t.co/IM2LhSckp6— John Hartson (@JohnHartson10) August 3, 2016
The Welshman knows a thing or two about European success and was part of the Celtic team that reached the UEFA Cup final in 2003, scoring crucial goals against Celta Vigo and Liverpool along the way.
Celtic's Kolo Toure in action
Celtic have so far added Moussa Dembele and Kolo Toure to their squad and while both are excellent signings, more is needed if the Hoops are to compete with Europe’s elite.
Aston Villa's Scott Sinclair in action as Watford's Juan Carlos Paredes looks on
The club has been linked to the likes of Scott Sinclair (by the Daily Record) and Paddy McNair (by the Herald) and business needs to be carried out swiftly if Rodgers is to have greater options ahead of the season-defining clash in a fortnight.
Who should Celtic sign this month?