Details of Nemanja Matic's downfall at Stamford Bridge were initially used as retaliation towards those at Old Trafford upon completion of his summer reunion with Jose Mourinho. Later, though, they would become painful reminders of the inconsistencies in his game.
The Serbia international was signed by Mourinho as the picklock to Paul Pogba's shackles, the holding player to collect the ball and distribute accordingly without breaking the structure of his team. However, those same traits he was acquired for have become his downfall.
The simplicity in how Matic performs extracts the little creativity United hold in their midfield and makes him look cumbersome when those around him are also without energy.
Matic's importance to Mourinho's side in the opening stages of the season, however, cannot be understated. He was everything that his manager asked of him. In his opening 11 Premier League appearances of the campaign, Matic made an average of two interceptions and two tackles per game and held a pass completion rate of close to 87%. He also claimed his only assist of the season so far.
And though the accuracy in his passing has not dropped, the urgency in his ball movement is now missing, and he looks largely untroubled when he is the cause of United giving away possession.
It follows a similar line to last season, in which the midfielder created the majority of his chances, dispossessed his opponents more, and generally had a much stronger influence on the game during the first half of the season.
The pragmatism Mourinho is known for contributes to Matic's lessening impact, with his recent shortcomings exaggerated by the lack of intensity elsewhere in the midfield. United's over-reliance on the 29-year-old is also a significant factor in his decline, having played more minutes than any of the club's other outfield players this season with just 11 games remaining.
United have now lost both of their last away league outings - 2-0 at Tottenham and 1-0 at Newcastle - without asking much of their opponents.
Wednesday's Champions League trip to Sevilla was presented as an opportunity for Mourinho to cleanse his squad of recent Premier League difficulties and to ensure the club had a genuine chance of progressing into the quarter-final stage of the competition.
Those who witnessed the game, however, were merely handed an extra serving of dross in the shape of a 0-0 draw.
And while Mourinho's tiff with Pogba nudged the spotlight away from Matic, the midfielder's performance was again a sticking point for many supporters.
Lined up in a midfield three alongside Ander Herrera and Scott McTominay, Matic was the instigator in what was quite blatantly a plan to stifle Sevilla and return to Old Trafford at least on par ahead of the second leg. Matic won more tackles (five) and made more interceptions (eight) against the Liga side than any of his United team-mates, yet was completely bypassed for large parts of the game.
“We have to be honest and say we’ve had some very good games," Matic said following United's draw in Seville. "But we’ve also had some bad games. We have to improve together. We have the Champions League and the FA Cup to play for. We have to fight until the end and we will see what we can do."
Mourinho is still unsure of how to structure his squad to ensure his attacking outlets correspond to other elements in the team, without bowing to external demands to release the team's handbrake.
Matic is something of a comfort blanket for the United boss, and to suggest that he will go into a game as big as Sunday's clash against Chelsea without the midfielder in his starting XI is irrational.
However, Matic absolutely owes United a performance against his former club to suppress the growing feeling of uncertainty directed towards him and his future at Old Trafford, and he requires a certain amount of sparkle from those positioned around him in order to achieve it.