Manchester United's No.7 shirt takes no prisoners... just ask Alexis Sanchez

Had Michael Carrick taken up Sir Alex Ferguson's offer, it could have all been so different.

In the weeks after Cristiano Ronaldo completed his £80million move to Real Madrid in 2009, Manchester United had the biggest of shirts to fill.

Carrick takes up the story.

"After he'd gone, the Boss offered me Ronnie's shirt," writes the former midfielder in his autobiography 'Between the Lines.' "He called me and Michael Owen in the office.

"'You can have No.7 if you want it,' he said to me. No.7 is a massive number at Manchester United. Best! Robbo! Cantona! Becks! Ronnie!

"When you look back at the players who have had it, it means a lot. But, as with the No16 and the Keane connection, numbers didn't bother me. And Owen said, 'I'll have it!'

"'Go ahead!' I said."

In fairness, no one has worn the most iconic of United shirts with such aplomb as Owen over what has been a turbulent nine years.

His dramatic late derby-winning goal in 2009 created another unforgettable moment in the history of the number worn by the club's greatest legends.

But Owen was never more than a fringe player at United – and he is one of a growing list of players who have failed to do it justice since Ronaldo's departure.

Had Carrick – United's Mr Dependable – taken it on, perhaps the heat could have been taken out of the situation. Even if the former England international suffered his own crisis of confidence as United began the post Ronaldo era, a man who willingly inherited Roy Keane's shirt, would not have been weighed down by the expectation of any number.

Instead Alexis Sanchez is the latest to have fallen victim to the curse of the No.7.

It is a measure of the Chilean's struggles at Old Trafford that his most significant contribution since his January move from Arsenal could be his part in a wage bill that has risen by more than 10 percent year-on-year.

Sanchez' salary, which is reputed to be as much as £500,000-a-week, was thrust back into focus last week following the publication of United's latest financial results.

Ed Woodward had used his February address to investors on the New York York Stock Exchange to brag about the number of social media impressions and shirt sales generated by the signing of the 29-year-old.

A look at Twitter on an average matchday this season will also find you numerous posts regarding Sanchez. But many of them will relate to his dramatic loss of form – or absence from the team sheet.

As for shirts, the big question is just how long Sanchez' name will adorn the No.7 at United.

He is as frustrated as anyone about his plight at Old Trafford, and a move could come as soon as January if the right offer arises.

With Anthony Martial realising his potential on the left of attack and in negotiations over a new five-year contract, the future looks bleak for Sanchez, who couldn't even make the starting line up in the absence of Romelu Lukaku for United's derby defeat to Manchester City before the international break.

With Lukaku expected to resume his place at the point of attack when the domestic calendar resumes this weekend, finding a role for Sanchez looks increasingly difficult.

The right of attack remains a problem for Jose Mourinho, but Sanchez has shown no indication that he can make it his own.

And with Mourinho still intent on signing a specialist right winger, Sanchez' opportunities in that role will be further limited.

So what has gone wrong for a player Pep Guardiola was desperate to add to his City attack?

Sanchez has been described as a lonely and isolated figure in Manchester. The recent breakdown of his relationship has also been tabled as a factor.

But those who know him insist he is not the type to be concerned if he has a lack of friends in the dressing room. Rather he is obsessed with matters on the pitch.

So long as life between the lines is going well, he'll be happy. Which goes a long way to explaining why he often looks so sullen these days.

Very little has gone right on the pitch since his arrival – and while there have been sparks of life, such as his late winner against Newcastle last month, they have been few and far between.

That remains his only goal for United this season.

He scored for Chile on Saturday, but a penalty miss in the same match summed up his lot at the moment.

And for a player who looks a shadow of the man who struck fear into the hearts of defenders during his time at Arsenal, the uncomfortable truth could be that his best days are now behind him.

Both he and United will hope a goal for his country proves something of a springboard. But the reality is, his best chance of starting against Crystal Palace on Saturday will be if Martial fails to recover from the adductor injury that forced him to pull out of France's squad.

It's a remarkable predicament for a player of Sanchez' reputation to have to handle, but all too familiar in the recent history of the shirt he wears.

From the superstar in Angel Di Maria to the rising star in Memphis Depay, United's No.7 takes no prisoners.

Woodward believed Sanchez would break that curse.

If anything, he's only confirmed it.