Mauricio Pochettino told Mykhailo Mudryk he "needs to improve" despite his goal-scoring display against Arsenal.
The 22-year-old winger extended Chelsea's lead as his cross flew over David Raya, adding a second after Cole Palmer's first-half penalty.
The Ukraine international was then the first player substituted by Pochettino in the 66th minute and the Blues boss explained he still expects even more from the £88.5million signing from Shakhtar.
"No, I think he is playing good but also he needs to improve still," Pochettino said. "For me he is not at his best.
"I think we needed to change and to put a bit more of pressure on with Nicolas Jackson up front. After that situation we created a few chances and I think the game was closer to 3-0 than 2-1."
Declan Rice pulled a goal back after a Robert Sanchez mistake but Pochettino refused to blame his goalkeeper for the result.
"We are so happy with him," he added. "Of course he is disappointed and upset with his decision but mistakes happen in football.
"This goal gave the belief to Arsenal. We can maybe read better the situation, the tempo, the timing. We can take risks on 77 minutes because it’s our philosophy, but maybe there is another decision you can take.
"It’s not to blame someone. It can happen. It will arrive with time, when to be calm and when to take risks, and we are still a really young team getting to know each other."
Leandro Trossard equalised in the 84th minute in what was ultimately a disappointing outcome for Chelsea.
"Of course we are disappointed at the end, but we can’t only look at the last few minutes," Pochettino explained.
"There were many positive things. We were the better team. We lost two points in a way you never want to lose them, but after playing a team that was fighting for the Premier League last season we can take many positives and be proud.
"We showed great character and personality. We were competitive, we deserved more, and we need to keep believing because good things will arrive. I like the way the players are feeling now. They are really upset. I want to see that. But we need to keep working. We are in a good way."
