World Cup winner Leboeuf, a former Chelsea and France defender, insists the major rebuilding job is the only way for the west London side to challenge again for major honours.
The emergence of Manchester City as serious rivals for Manchester United's Premier League crown, coupled with the form of Tottenham, Arsenal and Liverpool, has even raised doubts over Chelsea's chances of securing a top-four finish that would guarantee Champions League football next season.
Villas Boas, the 34-year-old boss recruited after guiding Porto to a trophy treble last season, has already made moves to freshen his ageing squad by accepting transfer requests from Alex and Nicolas Anelka.
But Leboeuf, a favourite at Stamford Bridge for five seasons, believes the pair shouldn't be the only senior players shown the door.
"Some players will have to leave, those who are getting told and who aren't playing, to bring some success back to Chelsea," Leboeuf told AFP in an interview here Friday.
"I think six or seven need to go and they need to be replaced," explained the 43-year-old, an FA Cup winner with Chelsea in 1997 and 2000.
"That might seem a drastic measure, but that's realistically what they need to do. Chelsea needs to move on and change.
"It's now about getting the right balance. For instance, Didier Drogba is still a very efficient striker, but you have to think about the future as he is 33."
But Leboeuf cautioned against ditching Chelsea captain John Terry and midfielder Frank Lampard even though the two England internationals have not always been at their best this season.
"You still need some experience and players like John Terry and Frank Lampard have been crucial for Chelsea for years. They might be getting older, but they are the symbol of the club.
"They represent so much of English football and will be useful for the new players. Others might not be."
The worst start to a season since billionaire Roman Abramovich bought Chelsea eight years ago raised doubts over Villas-Boas's future.
But Leboeuf said the Russian owner, who has appointed seven different managers during his ruthless regime, should give Villas-Boas more time to impose his ideas.
"He is young, but Chelsea knew that when they hired him," said Leboeuf, an ambassador for Premier League title sponsor Barclays.
"It would be stupid and make no sense if they got rid of him now. You need consistency. He must be backed up and must stay for a long period."
Despite playing catch-up in the Premier League, the Blues have at least extended their season by qualifying for the Champions League knockout stages.
But with a 10-point gap separating league leaders Manchester City and Chelsea, Leboeuf believes only ending the mega-rich club's unbeaten start to the season at Stamford Bridge on Monday will breathe life back into their title bid.
"They can win and I think they will surprise many by doing so," he added.
"You don't become a bad side overnight and you can't write them off.
"But I feel Chelsea need to win here if they are to challenge, if not they will have too much work to make up."