Sabri Lamouchi offered a stark warning to his Nottingham Forest players after seeing them suffer a 2-0 defeat at the hands of Cardiff.
Forest have now gone eight league games without a win after two goals from Kieffer Moore helped Neil Harris' side to their first victory of the campaign.
Lamouchi was furious after seeing his side concede twice from set-pieces, after spending hours on the training ground working on defending them over the past week.
Moore took only three minutes to head home a corner, before prodding home following a long throw-in five minutes before half time.
Forest's slide out of the play-off places last season saw him come under pressure and that scrutiny remains following two defeats in two league games this campaign.
"We started the game in absolutely the wrong way. It is just unacceptable to start the game like that, by winning absolutely no duels," said Lamouchi.
"We conceded a goal from the first corner and we knew the quality of this (Cardiff) team. We had worked all week on dealing with long throw-ins, second balls and corners. Our marking was absolutely unacceptable.
"We conceded the first goal from their first corner and the second goal the first time they launched a long throw into the box. You can work all week, but if you are not focused and determined, when it comes to defending those things, you do not have a chance.
"The second half was much better, because we did not play in the first half. But we have to do more. We have to be more solid, more strong. We were so soft, we made it so easy for the opponent. We need to find a solution to get out of this difficult situation.
"Some players are still thinking about the end of last season. But this is a new season and we have new players and we have the quality to get out of this situation.
"But the League has started. This is not a friendly game. This is the Championship and we need to have more aggression and determination. We cannot accept what happened in the first half of this game."
Cardiff manager Neil Harris was delighted to see summer signing Moore score twice.
He said: "I'm really pleased for the big man, he was desperate to come and play. So you're delighted when he gets off the mark with goals, his all-round performance was excellent, his athleticism too.
"The team showed a great response to a little bit of criticism as we hadn't started the season very well. I thought the focus, the mentality, on and off the pitch, it came to fruition here, especially in the first half.
"We spoke in the week about being better and more productive with the ball. In the first half, it was exactly how I want my Cardiff City team to play now and in the future. We weren't as good in the second half, but we dug in and got a clean sheet.
"It has been such a short turnaround, we did not have much time to work and then we have been back at it straight away, so we did not start great as a team, last week. Today we had quality in the final third, we kept a clean sheet and this was more like the way we want to play the game."
