It wasn't a scintillating performance from the 'Red Devils' in the first leg of their Champions League tie on Wednesday as they failed to dominate possession or chances against their Spanish opposition, with the match ending in a dull 0-0 scoreline.
The lack of cutting edge from a team who boasts big name players such as Paul Pogba, Alexis Sanchez and Romelu Lukaku is just one of a long list of issues which Mourinho must address before his team face Chelsea at the weekend, who are experiencing a revivial under Antonio Conte.
We take a look at some of these problems:
PAUL POGBA
The Frenchman is arguably United's biggest sticking point at the moment given increasing speculation of a rift between himself and the manager. He started on the bench for the Manchester club against Sevilla, but ending up playing the majority of the game after Ander Herrera limped off after 17 minutes, although he made little impact in an attacking sense.
In fact, Pogba only had one touch in the opposition box, but instead played a more defensive role, mindful of the danger of leaving too much space between himself and his two midfield partners (Nemanja Matić and Scott Tominay). However, it didn't stop him making nearly twice as many passes in the opposition half than his teammates.
The problem for Mourinho though is whether to utilise Pogba in a similar position against Chelsea. There's no doubt he will be a great physical presence in that midfield, with the 'Blues' not possessing a player of a similar stature there. Nonetheless, with a lack of creativity going forward for United at the moment, his athleticism and moments of genuis in a more attacking position could prove decisive.
SCOTT MCTOMINAY
The young midfielder put in an assured performance against Sevilla and appears to have Mourinho's complete confidence, starting in nine of United's games this season, though it could be a big ask to play the 21-year-old against Chelsea.
He managed to contain playmaker Ever Banega on Wednesday while completing 90 per cent of his passes. However, it will be a entirely different task against Eden Hazard et al. on Sunday, especially after the 'Blues' did so well against possession-minded Barcelona in their Champions League first-leg, suggesting that a more seasoned player could be a better alternative.
LACK OF CREATIVITY
United didn't look like scoring an away goal against Sevilla. They were only able to muster one shot on target throughout the whole 90 minutes with Lukaku's wild volley from a Sanchez's chipped pass their only notable opportunity.
It seems to be following a worrying trend for them, in which they have only scored four goals in their four games so far in February at an average of one a game - far below what you would expect from the 'Red Devils'.
Something needs to be changed ahead of the game with Chelsea as the 'Blues' looked a clear attacking threat against Barcelona, despite benching strikers Olivier Giroud and Alvaro Morata, and you would back them to bag a few on Sunday.
MARCUS RASHFORD AND ANTHONY MARTIAL
The duo have fallen slightly down the pecking order thanks to the arrival of Sanchez, however, one of them should arguably feature over Juan Mata against Chelsea to offer a more aggressive approach.
Out of the two, Martial has certainly been more effective this season, scoring nine goals and providing four assists in just 1282 Premier League minutes. Meanwhile, Rashford, you would argue, would be better utilised as an impact substitution.
THE DEFENCE
The back-line held up well against Sevilla on Wednesday and is one of the only positives from the game for United, although that doesn't mean there aren't problems. David De Gea was a key reason why the 'Red Devils' kept a clean sheet and with some erratic performances from Chris Smalling and Phil Jones this season at centre-back, could Mourinho opt with Victor Lindelof?
The Swede did not feature in the dismal loss to Newcastle United and has instead been part of two of three clean-sheet defences this month for the Manchester club. However, he is young (23) and relatively inexperienced and could end up being exposed by Hazard and Willian, although his selection could come down to whether Jones recovers in time.