The Swedish defender was heavily criticised for his performance as his blunder allowed Huddersfield Town to claim a famous 2-1 victory over the Red Devils in the Premier League on Saturday.
Lindelof came on as a first half substitute for the Red Devils after Phil Jones picked up an injury, but the defender struggled to gain a foothold in the game.
The centre-half has been far from convincing since his transfer to Manchester United from Benfica in the summer transfer window and he has seemingly struggled to adapt to the rigours of the Premier League.
And former Red Devils midfielder Hargreaves reckons that Mourinho will be quickly losing faith in Lindelof following his shaky displays in recent weeks.
Speaking on Premier League Tonight on BT Sport, Hargreaves said: “He’s really really struggled. Obviously at Benfica he played incredibly well in the Champions League, some great performances.
“But we saw him against Real Madrid in the Super Cup he really struggled and today, both goals he was involved in.
“He was thrust into action when Phil Jones went off injured and he’s come on and really really struggled.
“For Mourinho you have to earn his trust and I think today he’s lost some of that with his performance.”
Manchester United return to Premier League action next weekend when they take on Tottenham Hotspur at Old Trafford.
Saturday’s loss left Mourinho’s men five points behind leaders Manchester City in the race for the Premier League title.
MORE: Man United latest news
MORE: Arsenal latest news
MORE: Chelsea latest news
MORE: Liverpool latest news