Thomas Tuchel acknowledged Edouard Mendy's "huge" error cost Chelsea dearly after the 10-man Blues slipped to a demoralising 3-0 loss at Leeds United.
Mendy inexplicably allowed Brenden Aaronson to steal possession on the edge of the six-yard box and poke Leeds into a 33rd-minute lead.
Further goals from Rodrigo and Jack Harrison helped the hosts claim their first win over Chelsea since December 2002.
Kalidou Koulibaly was then sent off after picking up a second booking as Chelsea's miserable outing drew to a close. It was the defender's sixth league dismissal since the start of the 2017-18 season – more than any other player in the top five European leagues.
But it was Mendy's dismal mistake which put Chelsea on the back foot, and Tuchel did not hide his frustration with the Senegal goalkeeper after the match.
Asked whether he would discuss the incident with Mendy, Tuchel said: "He knows himself. With these kinds of mistakes, I don't think we need to speak a lot.
"He knows himself that this was a mistake and honestly, this has nothing to do with protection or no protection.
"Everybody in the world sees the mistake, it's a huge mistake in a crucial time of the match. It does not help and he's the one that is the most disappointed because it cost us a lot today."
60 - Today was Thomas Tuchel's 60th Premier League match; Chelsea conceded just 17 goals in the first 30 of these, but have shipped exactly twice as many in the last 30 (34). Concern. pic.twitter.com/aKLQCHRwbK— OptaJoe (@OptaJoe) August 21, 2022
Speaking to Sky Sports, former Manchester City and Newcastle United goalkeeper Shay Given was equally critical of Mendy's decision-making, saying: "He just has a really poor first touch and his head's a bit scrambled at that point. Worst case, kick it out for a corner, just don't do what you do.
"The only thing I would say in Edouard Mendy's defence, not too many Chelsea defenders have run into a position to receive the ball from him.
"But it's still a terrible mistake from Mendy, he knows he has to clear his lines. It's a poor, poor goal to give away."
The defeat at Elland Road represents another blow for Chelsea, who conceded a last-gasp equaliser against London rivals Tottenham in their previous match.
2013 - Brenden Aaronson is the first American to score against Chelsea in the Premier League since Jozy Altidore for Sunderland in December 2013. Tackle. pic.twitter.com/zp0C6VnxfI— OptaJack (@OptaJack) August 21, 2022
Leicester City defender Wesley Fofana has been strongly linked with the Blues as Tuchel bids to strengthen his defence, but the Chelsea boss insists his existing squad should be performing better.
"We need to wait. The transfer period is still open. It gets later and later and we need to focus on what we have and what we can do," Tuchel said.
"We can obviously play at a high level, but we lost track when there was no need. We were not forced to lose track. Everything was going well.
"We can win with this team in Leeds, everything was going well and we had goalscoring opportunities. It went the other way and I think it was more our fault than anyone else's credit."
While a defensive addition remains an aim, Tuchel was dismissive when asked whether Chelsea could target a new midfielder, responding: "Another midfielder? We have Jorginho, N'Golo Kante, we have Ruben Loftus-Cheek, Conor Gallagher, Mateo Kovacic.
"They [Kovacic and Kane] are injured, yes, it's a problem. But they will come back. They've not disappeared."
Chelsea host Leicester City in their next Premier League game on Saturday, having claimed four points from their three outings this season.