Lee Johnson has said Bristol City's first-half display in Tuesday's defeat by struggling Huddersfield Town was "as bad as I've felt" as head coach.
The seventh-placed Robins, who remain three points outside the play-off places, lost 2-1 to the Terriers.
It was City's third successive loss, with the performance prompting Johnson to apologise to the club's fans.
"I feel upset," he said. "As upset as I've been watching one of my teams with players I've signed."
Having risen as high as fourth after winning at Fulham on 7 December, Bristol City have struggled for consistency and have now lost nine of their past 15 Championship matches.
The defeat by Huddersfield, who are battling against relegation, followed losses to Leeds United and West Bromwich Albion, the top two in the table.
"It was a very difficult watch," Johnson told BBC Radio Bristol. "It was substandard.
"I feel a little bit sick in my stomach for one of the first times as Bristol City manager because I didn't like what I saw tonight on a number of levels in that first half."
Johnson made four changes to his starting XI, as well as switching to a back three, but kept faith with January signings Filip Benkovic, Markus Henriksen and Nahki Wells.
However, Benkovic and Henriksen were both substituted at half-time - and Johnson was critical of his new arrivals after the game.
"I think a couple of the new players need to have a look at themselves for different reasons and quickly get into the programme," he said.
"At the same time, it's a team game, including all of us, so I don't mean to dig them out.
"I don't want to lie and say it'll be easy to go from that first-half performance to beating Millwall at The Den. It can be done, but it comes from the inner sanctum of the player and that fire in the belly."