The Welshman was extremely critical of Neil Lennon's Hoops side who capitulated at Ibrox after leading 2-1 at half-time, handing 'Gers a four point lead at the top of the SPL table.
'Scared, weak and out of their depth,' Hartson wrote in his column for SunSport.
'Not the words I want to use to describe Celtic's team at Ibrox on Sunday.
'But Neil Lennon picked players incapable of dealing with Rangers. And it's time he came out and explained why.
'I take no pleasure from laying the boot into my old club.
'And this isn't a character assassination of my mate Lenny.
'There isn't a Celtic supporter out there hurting more than the wee man. But the harsh truth is the buck stops with him.
'And he made some decisions on Sunday only he can explain.
'The Celtic fans are the people who went a long way towards Lennon getting the job in the first place.
;So for me he has to come out and say why he went with the players he did. His team let him down and badly. They are the ones who deserve all the criticism flying around.
'But Lennon is the man who named the line-up and I can't understand some of the choices he made.
'They are the players the fans hold most responsible.
'If so, Lenny has to tell them why they were in the side. I certainly can't work it out.'