The Blues continued their stuttering start to the Premier League season with a disappointing 3-3 draw with Southampton at Stamford Bridge on Saturday.
Timo Werner put Frank Lampard’s side 2-0 up within 28 minutes with two smart finishes, but Havertz was dispossessed in a dangerous area as the Saints pulled one back through Danny Ings.
Che Adams then equalised, capitalising on a mix-up from Kurt Zouma and Kepa Arrizabalaga, and though Havertz tapped in his first league goal to make it 3-2, Jannik Vestergaard grabbed a late leveller.
£70 million signing Havertz has shown flashes of brilliance, such as his hat-trick in the 6-0 Carabao Cup win over Barnsley, but struggled to perform consistently.
Former Chelsea defender Leboeuf says he is yet to be convinced by the Germany international, but is happy with his compatriot Werner.
‘I’m not convinced about Havertz, I’m not that optimistic,’ Leboeuf told ESPN FC. ‘I’m very pleased with Werner, he’s a real satisfaction.
‘Thiago Silva should have been back because it’s crucial for Chelsea to have a real leader at the back and that’s the main problem. They all have to work hard physically to make sure they can play together and be stronger together.’
The Blues have picked up just two wins from their first five league games, and Leboeuf is concerned about his former side’s chances of finishing in the Champions League places if performances don’t pick up.
‘Im not convinced at all about Chelsea right now,’ Leboeuf added.
‘It’s like they don’t know each other, they’re not fit enough, I’m very worried.
‘I’m going to give them the benefit of the doubt because I don’t know what they’re worth, but, really, if they keep on performing like that, for sure they’re not going to finish in the top four.’