Thomas Tuchel insisted hauling off substitute Callum Hudson-Odoi at Southampton should not harm the player's confidence, telling the Chelsea winger to "swallow it".
Hudson-Odoi came on at half-time to replace Tammy Abraham, only to then be taken off in the 76th minute as Tuchel summoned Hakim Ziyech.
That change did not pay dividends, with Chelsea unable to complete the turnaround after Mason Mount had cancelled out Takumi Minamino's opener, with the points shared in a 1-1 draw at St Mary's.
During his time on the pitch, Hudson-Odoi had just 18 touches, attempted 10 passes – completing seven – and did not register a single effort on goal or create a chance.
Hudson-Odoi has been a success story of Tuchel's time at Chelsea so far, but the Blues boss insisted the 20-year-old must show an improved level and attitude.
However, Tuchel is not concerned that Hudson-Odoi's confidence will have taken a hit.
"No, no. Absolutely not," Tuchel told a news conference. "You have to understand that sometimes I take the decisions to win games. It is not a problem if he makes mistakes, has a bad game or misses a chance, but we cannot lack energy. It is not possible.
"I know what he can give and that's why I trust him a lot. This will not change, but he knows exactly what I demand from him. When he doesn't reach this level then maybe we have a hard decision like today.
"We don't need to think in old-fashioned terms that this is the worst thing that can happen. Okay, it happened today but it is already over and maybe he starts against Atletico [Madrid] where maybe we need his qualities, but he needs to be trusted and reliable and this is the next step for him.
"Always when he doesn't start, he is a bit in trouble when he comes on from the bench. It was like this against Sheffield United and today, he needs to improve on that because we need him from the bench.
"He needs to do it in a different way, now it is forgotten, he needs to step up, learn from it, swallow it and then there's no problem."
As has been customary under Tuchel so far, Chelsea dominated possession against Southampton, controlling 70.8 per cent of the ball.
However, that possession translated to just three attempts on target – including Mount's 54th-minute penalty – and nine shots in total, half the amount they managed against Newcastle United last time out.
Tuchel once again utilised a 3-4-3 system, but he does not believe the formation or structure of his team was to blame for their profligacy.
"We will work on it but you will score in any structure or concede in any structure," Tuchel added.
"The structure is never the problem or the solution. It is always the input of the players, the structure is fluid.
"We think day and night about scoring and creating chances, we play high up the pitch and the statistics from the last matches I know we don't score enough for the amount of touches in the box and the amount of creating.
"In the moment it is a lack of precision, not a lack of opportunities or lack of touches in the box.
"It is a lack of quality in decision making, today I did not feel in the last 10 metres that we would kill the game when it is there to be done. I will analyse and it is my job to create more or bigger chances."