Chelsea manager Frank Lampard believes there is more to come from Fikayo Tomori and admitted the young defender is a great example for the rest of his squad.
The 21-year-old received his maiden England call-up on Thursday after a strong start to the season.
Tomori, who spent last season on loan at Derby with Lampard, has made seven appearances and scored in the recent win over Wolves.
What has impressed his manager most, however, is the work ethic and training displays of the Chelsea academy graduate.
"You don't know until you put players in," Lampard said. "Sheffield United at home was a game where I thought he deserved his opportunity for his training. How he trained. That is a great message to all the players.
"How you train will relate to whether you get picked. Those are the rules here. You have to train at a level and he trained so well for a period of time he deserved it (his full debut). Then he gave me a big problem because he played so well and he has continued to do that.
"Yes, he is a project in a way but a nice one because everything you want him to do, he stands up and delivers."
After initially describing the centre-back as quiet, Lampard corrected himself and discussed the popularity of the Canadian-born defender in the dressing room at Derby last season.
Tomori was the Rams' player of the year for the 2018-19 campaign and his focus and desire to improve immediately caught the eye of his current boss.
Now England is calling, but first the one-time Brighton loanee will need to keep up his level of performance when Chelsea travel to Southampton in the Premier League on Sunday.
"At the moment, he has really delivered and long may that continue, but I think there is a lot more to come still," Lampard added.
"They know where the staff are at – it's not just me – we drive it hopefully daily and the minute we see any standards drop daily, or in a game, we would try and get on it.
"Now they're young players so we can't be too harsh because we know there must be sometimes some patience there, but in terms of application and all those things, then we can be harsh about it and to be fair all the players at the moment have shown that.
"Tomori shows it – it's a good example to play so well against Liverpool and Mo Salah, who is a fantastic player, and against some really quick Lille strikers.
"Now I want to make sure he switches straight back on like he did against Brighton and like he hopefully will against Southampton and in the games going forward."
Against Lille, Tomori was part of a Chelsea back three, but during the Champions League tie Lampard switched back to a four-man defence.
He wants the Blues to be "adaptable" and able to change formation mid-game if needed and also discussed his policy of giving young players a chance.
Several Englishman have featured for Chelsea this term, with 1,797 minutes given to players eligible for England – it took them 32 games to reach that mark last season.
But Lampard insisted: "It doesn't matter whether you're an English 20-year-old or a French 20-year-old. I think if the ethics are right and you deserve your place in the team, you'll get your place in the team.
"Yes, it's obviously a nice story because fans really do enjoy seeing the young English boys coming through and they all have an affiliation with the club.
"But then if you look below them slightly, you have Ian Maatsen who is a young Dutch boy, a really good young player. If he comes through I would feel exactly the same so it's nice to see."
Chelsea's England quartet of Tomori, Ross Barkley, Mason Mount and Tammy Abraham are expected to feature against Southampton.
