Steve Evans has issued an "unreserved apology" to fans for Rotherham's performance in Saturday's home defeat to Southend.
The Millers crashed to their fourth league defeat of the season - their second at New York Stadium - and are now 13th in the table, four points off the top seven with a game in hand.
"It was awful from start to finish," said Evans, who has now completed his six-game stadium ban imposed the Football Association for using foul and abusive language towards a female Bradford match steward when in charge of Crawley last March.
He added on the club's official website: "For me there was a distinct lack of effort, which in football is unforgivable. As a team and as individuals we lacked energy, desire and our performance had no passion.
"When all those characteristics are lacking in a performance then you have no chance of getting any positive result out of that particular match, ability never comes into it.
"As the manager I take the ultimate responsibility and rightly so. I will not have it any other way so I offer an unreserved apology to our supporters for Saturday's inept display."