Glen Johnson has questioned Liverpool's decision not to address their lack of options at the back in the January transfer window.
The Premier League holders have been without Virgil van Dijk since the Merseyside derby back in October, while his centre back partner Joe Gomez is pushing for a return before the end of the season after knee surgery in November.
Jurgen Klopp has relied on Jordan Henderson and Fabinho at times to drop back into defence, as well as youth options such as Rhys Williams, but Johnson believes Liverpool have made a mistake with their inactivity.
'I think they were naive in not getting someone in on loan because the kids - who will hopefully go on to be some fantastic players - are being asked to fill the shoes of van Dijk and that's not easy for anybody,' he said, speaking on behalf of Cheltenham Guides.
'The only options they had was to work with the youngsters or get somebody else in on loan and they opted to go with the youngsters and some have been great and some don't look like they're ready.
'They've tried a lot of personnel there and at the start they were doing fine but then if a player is playing out of position for too long, they can get found out.
'The odd game here and there is absolutely fine, but you're going to get found out eventually if you try to win the title with two midfielders playing a centre back.'
Johnson spent six years at Anfield before leaving the club in 2015, just a few months before Klopp arrived.
The 36-year-old believes his former side face a challenge just to finish in the Champions League places this season, let alone defend their Premier League title.
'I don't think Liverpool will have enough to win the league this year, but I expect them to get the top four - but it will be tough,' he predicted.
'It will be super harsh for Klopp to be under any pressure given the success that he's had, but we know that once owners get success they want to keep repeating it.
'I think there would be a discussion to have if he did finish outside the top four, but I think it would be extremely, extremely harsh in terms of where he's brought the club in the last few years.
'I don't think he would be sacked, but I think they would have a serious chat about it.'