Chelsea head coach Maurizio Sarri fears piling pressure on Callum Hudson-Odoi could lead to the winger losing focus and failing to fulfil his potential.
Fans at Stamford Bridge had called for the 18-year-old to be brought on ahead of his 78th-minute introduction.
But Sarri, whose team went two goals up thanks to strikes from Pedro and Willian, feels supporters and the media need to be more patient.
— Callum Hudson-Odoi (@Calteck10) March 7, 2019
"I think to have pressure when you are 18 is very dangerous for a player," said the Italian.
"You can lose the target. When you're 18 the target is to improve – to improve, tactically, mentally and physically.
"So, it's dangerous for him. I don't like to speak about him for this reason.
"Now I think we need to improve without the pressure of the media, without the pressure of the fans, without the pressure of the club."
Hudson-Odoi, who finished emphatically following a back-heel from fellow substitute Ruben Loftus-Cheek, handed in a transfer request in January amid offers from Bayern Munich.He has now scored four times this season but is still awaiting his first Premier League start.
Sarri insists Hudson-Odoi is in contention to play in every game and described him as a "very great player".
"He is in my mind for every match. In England, I think he's the only to be born in 2000 to have played 16 matches in the first team," said Sarri.
"He (doesn't) have to do anything to convince me because I am convinced that he is a very great player.
"I have my opinion. In my opinion a player at 18 years cannot be at the top yet. He needs to improve because he will be able to arrive at the top only at 22 or 23, like every other player."
Despite the resounding scoreline, Chelsea should have won by a far bigger margin with Pedro in particular guilty of being wasteful in front of goal.
Sarri accepted his team should have secured a greater aggregate lead but was satisfied to prevent Kiev grabbing an away goal ahead of next Thursday's second leg in Ukraine.
"Especially in the first half, we could have scored more. But the result is a good result," he continued.
"We were able not to concede a goal at home, which is very important in this competition.
"So the result is OK now. We have to be careful. We have to play the second leg and go there with a very good level of attention and application, if we want to qualify."
Dynamo manager Aleksandr Khatskevich admitted the match was a step up in standard for his team and hopes his players can regain some confidence ahead of the return meeting.
"The intensity was totally different compared to the Ukrainian championship," he said.
"On Sunday we are playing Arsenal Kiev, it's almost English week for Dynamo Kiev. I hope that we will beat Arsenal Kiev and have a good mood to go into the second leg."