Every big club has its own Achilles heel, no matter the number of riches it possesses. For City it's defensive midfield where there is no back up to Fernandinho; for Chelsea, it's Alvaro Morata; for Liverpool and Spurs it has always been trophies and as for Arsenal, it's their inability to perform against the rest of top six.
Having an Achilles Heel is nothing to be ashamed of, but doing nothing to repair it is. While the rest of the big six, particularly Liverpool, have moved swiftly to address their issues, Manchester United seem to have been complacent about theirs.
It was baffling to see United once again not going for a right winger when Antonio Valencia was the last successful player at that position, and he, at the age of 33, now plays at the right-back position.
Since then many have occupied the position to varying degrees of success but none have made the spot their own. The lack of speed on the right side has proven to be the undoing of United in many tight matches.
United have had a poor start this season which has forced Mourinho to be uncharacteristically creative playing Herrera and McTominay as part of a three-man defence and Pogba as a sweeper against Newcastle last week to varying degrees of success with Pogba proving to be a revelation in the deep midfield role but Herrera and McTominay resembling what they were - a central midfielder playing in defence.
Rashford, Mata, Sanchez and the currently injured Lingard have all occupied the right wing slot this season but none of them has performed satisfactorily forcing Mourinho to chop and change.
A big part of United's issues though stem due to the poor form of Lukaku at the club level. He is United's top scorer this season with 4 goals from 8 matches but stats do lie; he has been guilty of missing several chances in every match so far, which has proved very costly for the team.
He missed an open goal and pulled another shot wide against Spurs when the score was still 0-0. He was also guilty of throwing away chances in the loss against Brighton and the narrow wins against Burnley and Watford which would have put the game to bed.
But as Mourinho rightly said, Lukaku should not only be judged on goals as he is not your normal striker - he does not wait in the box for tap-ins; he drops deep regularly to collect the ball and spread it wide to pull the opposing defence out of shape so the wingers can drive at them with pace. For a bulky frame, he is surprisingly quick and has a wonderful passing range.
Last week against Newcastle where he drifted to the right wing and played better which also allowed Martial and later Sanchez to take up a central role, which eventually proved the difference provide an insight into his all-around ability.
Playing in the right-wing role would not be alien to him as he regularly drifts to the right when playing as part of a two-man strikeforce at United dragging one of the centre-backs with him creating space for the attacking midfielder, generally Lingard or Mata.
He has the pace, trickery and defensive know-how required to thrive as a right winger where he could either cut in and shoot or provide a cross for either Martial, Rashford or Fellaini to make the most of.
This would also shoot up his confidence which he is badly lacking now and would also allow Martial, who is being wasted on the left-hand side to flourish in his favoured central position as he is also the best finisher at United currently.
The season can't get any worse for Mourinho and Lukau as both are in desperate need of a spark and this positional change could benefit both and the team. Also, it can provide at least a temporary relief to the Achilles Heel that has been plaguing United for the last few seasons.
Mourinho has already tried out of the box solutions to fix United's defence and it's time he thinks out of the box to fix United's misfiring attack too.