Chelsea manager Thomas Tuchel says it was impossible for the club to sell Callum Hudson-Odoi.
The Englishman was pursued heavily by Borussia Dortmund, but Tuchel ultimately blocked the move.
Speaking after the 3-0 win over Aston Villa on Saturday, Tuchel heaped praise on Hudson-Odoi after his performance at wing-back.
Asked about keeping Hudson-Odoi in his squad, Tuchel said: "It was a very easy decision for me, we cannot let the player go who is in an 18, 19-man squad. Simply impossible.
"He is able to play as a right wing-back, left wing-back, he can play in these extra positions, he knows the group and we know him very well.
"For him personally it would maybe have been a very good opportunity but for us it was simply impossible."