The 18-year-old, who handed in a transfer request in January after Chelsea rejected a £35m bid from Bayern Munich, is keen to stay at the club.

Sources have told BBC Sport that he has agreed a new deal, but Lampard says there are still details to work on.

"If he had agreed then that would mean he had signed and we're not quite there yet," the new manager said.

"But it's very clear that the club are working towards that. I think talks have moved on very well in the last week or two, hence why the headlines came out, but it's not done yet.

"The one thing that's clear for me is I know I want to keep him here and the club wants to keep him because he's a player we cherish. He's come through our academy, he's the present and the future of this club, so we're doing everything we can to get there."

The teenager, who is recovering from an Achilles injury suffered in April, is on track for a quick return to action, potentially as soon as September.

Lampard, who has overseen new deals for young Blues players Mason Mount and Ruben Loftus-Cheek, said Brazilian winger Willian is also in talks over a new contract.

The 30-year-old has one year left on his current deal.

"I know the club are talking to him," Lampard added.

"Willian and Callum are both players I want in my squad. We've made some good moves this pre-season with Mason Mount and Ruben Loftus-Cheek signing new contracts - two young players nailed down and the club are always trying to do that.

"From a football sense, I've made my ideas very clear. I'm working very closely with Marina [Granovskaia, Chelsea director] and the board because these are two players that we want to stay for sure."