Frank Lampard has praised Fikayo Tomori and challenged the Chelsea defender to prove himself as a first-team regular.
Tomori played at Derby on loan last season under Lampard, who promoted him to the senior side after taking over at Stamford Bridge.
The defender has impressed and has been rewarded for his performances with a new long-term contract.
But Lampard has told him he still has plenty to prove and needs to keep working hard.
Speaking at a press conference, Lampard said: “He’s come a long way. He’s shown the work ethic – a want and a desire to listen and improve himself.
“I think everyone saw his performances (on loan) in the Championship last year – Derby player of the year.
“But then there were big question marks over him in the summer. Can he do it in the Premier League?
“Now, he certainly hasn’t proved that yet over a period of time, but from my point of view I had full trust in him and he’s done really well.
“I’m delighted for him – for where he’s got. The important thing now is that he doesn’t take anything for granted.
“Even though he’s got that nice contract, it’s important now that the hard work starts again. But I’ve been delighted with what I’d done.”