Thomas Tuchel says Callum Hudson-Odoi needs to replicate the ability he demonstrates in training in matches for Chelsea.
And the Blues boss is adamant the youngster can play in the right wing-back role he has often been deployed there since Tuchel took over.
But Tuchel insisted: “Callum has to overcome the gap between training and games.
“I see a stronger and stronger Callum every day in training and he needs to overcome this gap and show the kind of determination he shows in training.
“I know that it’s not his favourite position, but I think he can play in this position and serve the team when it’s necessary.
“Today it was necessary and still he can do better. Still he can be more aggressive and he needs to push himself absolutely to the limits – this is what he does in training and he needs to overcome this gap.”
Borussia Dortmund wanted to sign Hudson-Odoi on loan during the final stages of the recent transfer window.
Tuchel blocked the move – and says it was not a difficult decision.
The German said: “It was an easy decision for me on the last day of the transfer period – we cannot let a player go who is in an 18 or 19-man squad. It is simply impossible.
“He is able to play as a right wing-back, a left wing-back and the number 10 positions, he knows the group and we know him very well.
“For him it (a loan move) would have maybe been a good opportunity, but for us and our targets that we want to achieve it was simply impossible.”