United fired a blank last weekend against Crystal Palace and have now failed to win in their previous three Premier League matches, though Mourinho has highlighted where he think the problems in his squad are.
Whilst United can't move off a goal difference of -1 (-1!), their fans have had to watch rivals Manchester City once again score an abundance of goals, at 43, nearly double the tally United have wracked up, and top the EPL table.
Romelu Lukaku and Ander Herrera restored parity before the break, but United were unable to find a victor during an underwhelming second half performance during which Pogba repeatedly conceded possession, much to the visible frustration of his manager.
With the result, United are confirmed to remain in the seventh position for the current gameweek but their six-point gap to the top-four should certainly increase with Chelsea, Tottenham and Arsenal to feature on Sunday.
Mourinho made five changes to the side that beat Young Boys in the Champions League, with injuries forcing the Portuguese to deploy three central defenders.
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"We don't have many - I hope people understand what I mean - we don't have many mad dogs, who bite the ball all the time". "In the second half we went back to losing too many balls in midfield".
"It doesn't matter the system we play, it has to do with the characteristics of the players".
After turning the match on its head, United teams of old would have found a winning goal, but Mourinho's men seemed to lack urgency and mustered just one shot on target after halftime. Their opening 20 minutes looked as if they were not one of the attacking-wise worst teams in the league over the past 18 months.
"Second half there was not a lot of momentum generated by United, that's credit to us", Southampton manager Mark Hughes said.
Nathan Redmond had one of his best performances this season come against Manchester United.