Manuel Pellegrini has warned West Ham's young stars Declan Rice and Grady Diangana they have not arrived in the big time yet.
Academy product Diangana was last week rewarded for breaking into the first team this season with a bumper new six-year contract.
The 20-year-old winger followed in the footsteps of fellow youngster Rice, who signed a five-and-a-half year deal last month.
Hammers boss Pellegrini is delighted to see the club's youth system bearing fruit but has told both players they are at a "dangerous" stage of their careers.
"Diangana deserves it, he has taken a step with the squad of our team – he was in the under 23s before and now he is working every day with our squad," said Pellegrini.
"I think he has a lot of quality and we will see an important player in the future of this club.
"Now his development will depend on his ambitions and his mind, to try to improve every day.
"I try always to tell young players that they are in the most dangerous part of their careers, when they think that they have arrived but they have not arrived yet.
"They have started arriving, but they must improve every day working with professional players.
"Fortunately for me in all the teams I managed before I've had young players to try to develop their qualities. I hope West Ham will be exactly the same.
"Declan started improving a lot, he played last season, now we have Grady to help to be an important player for West Ham."
Diangana and Rice will be involved when West Ham head to AFC Wimbledon in the FA Cup fourth round on Saturday evening.
The Hammers have not lifted a trophy in 39 years and, sat in mid-table with neither Europe or relegation on the agenda this season, they are pinning their hopes on a cup run.
"I think that all the teams, when you start the competition, must have that winning mentality and think that you can do it," added Pellegrini.
"It is a different competition, one-off games, so anything can happen. Of course we want to try and continue as far as we can.
"We are not thinking about winning it, when you want to win something you must go game by game. We must try to continue for the next round.
"You always need a little bit of luck in the draw, now we must take it step by step."
