Joe Cole says Billy Gilmour “cannot afford” to play as badly as he did in Chelsea’s 1-0 FA Cup quarter-final win over Leicester.
The 19-year-old was one of three players replaced by boss Frank Lampard at half-time. Reece James and Mason Mount were also hooked.
Chelsea then improved in the second half, with substitute Ross Barkley grabbing the winner at The King Power Stadium.
Former Blues star Cole told BT Sport: “I have no doubt the young players will deal with it I am a massive fan of Billy’s.
“It was his first time playing in the number eight role and the game was very hectic.
“He was a little bit lethargic and that lesson needs to be learned.
“He is so talented but he cannot afford to play like this.
“They need to know what it takes to give Frank Lampard levels of play.”
It was a tough day for Gilmour, who previously impressed for the first team.
He earned rave reviews for his display against Liverpool but it was a different story on Sunday. He gave the ball away a number of times during the first period.
“It was one of those games where I had to do something,” Lampard said.
“They (the youngsters) will be top players for this club and have good careers but if I have to do something in games I will do.
“They will take it on the chin. We must learn from the mistakes.”