Bayer Leverkusen visited Celtic Park in the Europa League on Thursday night and scored a comprehensive 4-0 win over Celtic.
The Bhoys have conceded eight goals in their two Europa League group stage games so far, while in the Scottish Premiership they have conceded five times in seven matches, to sit six points off league leaders Rangers.
Hartson feels that asking Postecoglou to change his approach depending on the opposition is pointless, especially as when Celtic have their best eleven on the pitch he thinks they look a good team.
The Celtic legend believes that to make Postecoglou’s approach work, the club need to back the manager and bring in better defenders.
“Ange is not going to change his approach”, he wrote on Twitter.
“When Celtic field their best 11 players they look a good team.
“We have to back the manager our issue is we need better defenders that can defend for their lives with a bit more savvy.
“Leverkusen blew us away defensively.”
Celtic now have serious work to do in the Europa League if they are to still be in the competition into the new year, while a third place finish would see them drop into the Europa Conference League.