Jose Mourinho said Ruben Loftus-Cheek was replaced at half-time against Aston Villa because he was not pulling his weight defensively.
The 19-year-old was handed only his third Premier League start in the 2-0 victory, one of five changes Mourinho made following the recent defeat by Southampton.
The teenager began well, making strong runs from deep and seeing a deflected effort drop just wide.
But Mourinho felt he was found wanting in the holding role and he was replaced at the break by Nemanja Matic.
The Chelsea boss said: “He is brilliant with the ball. He doesn’t look 19 – he looks solid, stable and mature.
“But without the ball he doesn’t look as good tactically. I wanted more stability defensively.
“I see him playing there [in the holding role] when he has the defensive ability to do that.”