The Red Devils were drubbed 4-1 by the Serie A side on Wednesday in a crushing Champions League loss that leaves them 22nd in the league phase table after three games.
It takes United’s run of matches to seven without a victory in all competitions, and fans began to turn on the head coach after the full-time whistle, with calls for Carrick to be sacked on social media.
Facing reporters afterwards, Carrick emphasised that his side’s showing was “unacceptable”.
“I’m bitterly disappointed,” he said. “I’m frustrated, more than frustrated, I’m really angry to be honest.
“You’ve got to move on and think about what’s next. For us to play in that way is not acceptable, it wasn’t a good performance at all.”
Apology: Michael Carrick
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The under-fire United head coach remarked that he wanted a repeat performance of what his team produced in the 1-1 draw at Leeds United over the weekend.
However, the levels were nowhere near the standard expected of a side of United’s side, as they were second best to Cesc Fabregas’ men all night.
“That bit of intensity, spirit, aggression and willingess to give everything [was not there],” he continued.
“It was the total opposite of a performance, I have to say, and it was tough to watch.”
United return to Premier League action on Sunday when they host Bournemouth.
They sit 13th in the English top flight, and haven’t won since August, when they beat Ipswich 5-2 at home.