Leboeuf believes Havertz may not start the game after a lacklustre display in his debut against Brighton.
"You need sometimes [time] to adjust and I can accept that," Leboeuf told ESPN FC. "The problem is you have a big game against one of the contenders and you're going to play at home.
"If you lose the second game of the Premier League against Liverpool, it's going to tell you what you're going to expect for the rest of the season.
"So I think Frank Lampard should line up the players who are ready, who are ready to compete. If Havertz is not ready, if he's physically not ready, he shouldn't play because it's a big game that they have to play on Sunday.