Liam Rosenior admitted Chelsea are in a "difficult place" after Sunday's dismal 3-0 defeat against Manchester City piled pressure on the Blues boss.
Rosenior's side conceded three times in the second half at Stamford Bridge as Nico O'Reilly, Marc Guehi and Jeremy Doku netted for title-chasing City.
Chelsea are languishing in sixth place in the Premier League, four points behind fifth-placed Liverpool in the race for a top-five finish.
With their hopes of qualifying for the Champions League hanging by a slender thread, Rosenior is facing pointed questions about Chelsea's struggles since he arrived from Strasbourg to replace Enzo Maresca in January.
Chelsea have lost five of their last six games in all competitions, including three in a row in the Premier League.
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In those three league defeats Chelsea have failed to score and Rosenior said they had fallen well short of the standards he demands.
"Not good enough in the second half. It's a similar story for the past month now in terms of dealing with set-backs," he said.
"If you go down against teams as good as this, what you have to do for the next five minutes is to stay in the game. It ended up being a really, really difficult second half."
Chelsea were booed off at fulltime and Rosenior knows he can expect further criticism from frustrated fans if results don't improve in the final weeks of the season.
"I am accountable. This is a group. It's something we need to improve. It starts with your habits and values. I can't say there was a lack of effort. But there was a lack of confidence in the second half," he said.
"We have to improve. We are in a difficult place at the moment and we have got another huge game next week.
"We can't forget that we were playing against a team in massive form pushing for the title. But we need to win games like this. That's why I have come to the club."
Chelsea midfielder Enzo Fernandez was missing from the team for a second successive game after Rosenior's controversial decision to suspend him.
Fernandez angered Rosenior by hinting recently that he would be willing to leave in the summer.
But the Argentinian will be allowed to return to action next week after talks with the rest of the squad.
"Any team will miss Enzo. Myself, backed by the leadership group and sporting directors, made a decision for the long-term of the club," Rosenior said.
"Enzo wanted to have a conversation with the main players of the group. He has spoken with me, the leadership group and all of the players.
"There's nothing personal with Enzo. He will be back with the group on Tuesday. He is a top player and a really good guy."