The Sun says Senderos broke down and cried after the Gunners' Champions League 4-2 defeat at Liverpool last week.
Boss Arsene Wenger gave him a couple of days off to pull himself together but he was left out of the squad at Old Trafford.
The Swiss defender was blamed for Sami Hyypia's Kop equaliser in the Anfield defeat.
An Arsenal insider said: "Senderos seems to have gone mentally at the moment. He is in a bit of a mess.
"He knows he did not play well at Liverpool and feels responsible.
"The manager tried to talk to him but he is struggling to get his mind right again."