Notably, the Red Devils have gotten off to their worst start in 29 years as they were handed a 3-1 defeat by West Ham United at London Stadium on Saturday, September 29.
United have a tricky week before the second global break as they host Valencia in their Champions League group-stage outing before welcoming Newcastle United next Saturday.
While Mourinho has been grumbling about his lack of backing in the summer transfer window, he was able to pay 35 million pounds (then $48 million) in January for Sanchez despite being a free agent six months later.
Mourinho had dropped Alexis Sánchez and Jesse Lingard from the squad and picked Scott McTominay on the right of a back three.
Even West Ham reveled in United's problems before kickoff with an on-pitch discussion about United's tricky week.
Manchester United have not won the Premier League title since their famous final triumph under Sir Alex Ferguson in 2013.
"This time, it was not a linesman mistake, it was a referee mistake", said Mourinho.
"We were not good enough to stop the counter-attack". Second half we took time to react.
West Ham took just five minutes to open the scoring with record signing Felipe Anderson producing an audacious back-foot flick.
United now has three losses in the league after seven matches, when last season the team had seven losses in 38 games. But he did admit defensive errors were to blame for Yarmolenko's shot looping into the top corner off Lindelof just before half-time. Games like this we should be dominating, creating chances, showing people why we deserve to play for Man United and that didn't happen.
But hopes of a comeback flickered only briefly.
Meanwhile, club great Rio Ferdinand has hit out at Mourinho and expressed his frustration at the insipid performance against West Ham. Mark Noble was able to thread a pass through to Arnautovic, who evaded Chris Smalling before striking past De Gea.