The ex-Chelsea ace has warned PSG boss Laurent Blanc against using the 27-year-old at the back, arguing that the centre-half "goes missing" far too oftenParis Saint-Germain's decision to sign David Luiz as he feels the Brazilian has proven to be too unreliable to play in defence.
PSG paid Chelsea €50 million to lure the versatile centre-half to the Parc des Princes, but Leboeuf fears that the Ligue 1 champions will come to regret the transfer.
"I think that David Luiz has a lot of qualities. But he alternates good moments with spells where he goes missing entirely," Leboeuf told RMC.
"He is not a defender. The fact that Jose Mourinho put him in midfield at Chelsea is an indication that he wasn't convinced by his defensive ability.
"The problem became quite obvious at the World Cup. He was playing up front rather than in defence after just three minutes of play in the semi-final against Germany. That's the thing that scares me."
The 27-year-old started his professional career with Vitoria and also wore the Benfica jersey before joining Chelsea in January 2011.
He signed a five-year deal with Paris Saint-Germain earlier this summer.