However, injuries to Anthony Martial and Jesse Lingard mean a contribution from Sanchez, who has been on the fringes for most of the season under both Jose Mourinho and then Ole Gunnar Solskjaer, is now badly needed.
The extent of the muscle injuries to the two wide forwards, suffered in Tuesday's 2-0 defeat by Paris St Germain in the Champions League, isn't yet known but United have two crucial games coming up in the next 11 days.
On Monday, they take on Chelsea at Stamford Bridge in the fifth round of the FA Cup and then on Feb. 24 they host Liverpool in the Premier League.
The injury to Lingard meant that Sanchez came on just before halftime against PSG. The Chilean's performance provided scant confidence that he will be an effective replacement in those two fixtures.
"He's hardly touched the ball in the second half. He's definitely short of confidence. He's not the Sanchez we fell in love with at Arsenal," former United defender Phil Neville told BBC Radio 5 Live.
"He looks like someone who needs 10-15 games without coming off. I'm bereft of any excuse as to why his form has dipped. When you're looking at subs to come on and make an impact, he's probably not the one...
"They talk about Ole giving players love. He's got to be the one he gives love to now because of the injuries," Neville added.
But when Solskjaer was asked what he could do to get Sanchez firing on all cylinders again, the Norwegian made it clear it was down to the player.
"I can't do anything about Alexis Sanchez. When he plays he needs to find himself because we know there is a quality player there," the caretaker manager said.
LACK OF PACE
Sanchez, who has scored just three league goals for United, often slowed play down and was unable to produce the tricky and pacy runs that characterised his play at Arsenal, where he scored 60 goals in 122 Premier League appearances.
Solskjaer made no attempt to disguise the fact that United looked far less effective with Sanchez and Juan Mata on for Lingard and Martial.
"That's the reality, that Jesse and Anthony have been big parts of our squad and second half we didn't have the pace and movement to get in behind them," he said.
Whether Solskjaer or somebody else is put in permanent charge, there is expected to be movement on the playing staff and the 30-year-old, reported to be earning 1.4 million pounds (US$1.81 million) a month, would surely be top of the exit list.
A move is unlikely to be something that Sanchez would oppose.
He has not enjoyed life in the North West of England and in November, The Times reported that the break up of his relationship with Chilean actress Mayte Rodriguez "deeply affected" him and left him feeling "lonely, bored and ignored".
A fresh start may be what he needs to save his career and Tuesday signalled that there is life after Old Trafford.
Argentine Angel Di Maria had a disappointing spell at the club and was reminded of that when he was booed by United fans - but he showed his quality over the 90 minutes setting up both PSG goals.
