Monday night saw another disappointing performance from Manchester United as they crashed out of the FA Cup in a 2-1 defeat to Arsenal at Old Trafford; throwing away their only chance of silverware in the process.

The performance, as well as the team selection from United boss Louis van Gaal, posed further questions and concern about the fortunes of the Red Devils, who look to be set for an almighty scrap for a top four finish. To rub salt into the wound, it was a former player and boyhood fan of the club Danny Welbeck who netted the winner to send Arsenal on their way to Wembley once again.

With many pundits and fans stating the need for more money to be spent, it’s conceivable that United could rue the fact they don’t have some of their old players to call upon as the pressure grows to get results. And with many of their stars misfiring, there’s no doubt some of their former squad members would walk into the side at this present time.

In light of these problems, here are FIVE players Man United should never have let leave...

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Danny Welbeck

ClickWelbeck

It was widely noted that former United man Danny Welbeck celebrated his winner against his old club, and to be honest with you, who can blame him? Depsite his love for the club, Welbeck was told in no uncertain terms that he had no future at Old Trafford, with Van Gaal of the belief that the youngster didn’t have the quality required to score the goals United needed.

But given the chance upfront, Welbeck has shown he will score goals, and his willingness to play out of position in a wide area is something that United could well still do with. Given some of the performances put in by United’s star players this season, the decision to let Welbeck leave looks stranger every week.

Paul Pogba

Paul Pogba (France)

Despite numerous options in the middle of the park, United continue to be linked with a new central midfielder, with a certain characteristic missing from their side. They are in desperate need of a player who can attack as well as defend, a box-to-box player who can influence their team just like Yaya Toure does at Manchester City. Frustratingly for United fans, Paul Pogba looks to be just that man.

Always tipped as a promising talent, Pogba left United again after finding first-team options limited, something he would have no such worries over now. The Frenchman has become one of the top young midfielders in Europe since joining Juventus, and and just like Welbeck; found himself on the scoresheet last night as Juve extended their lead at the top of Serie A. There’s little doubting the fact he would walk into Van Gaal’s side today, and is certainly 'one that got away'.

Gerard Pique

Pique Gallery

To say Gerard Pique has won a few trophies since his Old Trafford departure is somewhat of an understatement. He has won the lot. A World and European champion with Spain, and a Champions League winner with Barcelona, the central defender has excelled since leaving Manchester.

A solid no-nonsense defender who is comfortable with the ball at his feet, Pique is just the player United fans would like at the heart of a back four which has been suspect in recent times.

At the time they may have felt he wouldn't cut it at the club with opportunities limited, but make no mistake, he would be a welcome part of the current squad.

Carlos Tevez

Carlos Tevez

Man United fans could be forgiven for feeling there was still plenty more to come from Carlos Tevez before he left Old Trafford. A Champions League winner with the Red Devils, the Argentine striker found it difficult to hold down a regularly position in the United team under Sir Alex Ferguson, and subsequently came back to haunt the club after moving to their city rivals and winning the Premier League in 2012.

Now plying his trade in Italy with Juventus, the 31-year-old already has 21 goals to his name this season, and would surely be welcome in a United side lacking goals – and apparently a 20-goal-a-season forward according to their manager.

Cristiano Ronaldo

Cristiano Ronaldo 1

Cristiano Ronaldo made his name during a sparkling six seasons at Old Trafford where he developed into one of the world's greatest players. He won all there was to win for the English giants, before following his dreams and making a record-breaking £80 million transfer to Real Madrid.

Since then, Ronaldo has raised his game even more, and his astonishing goalscoring record saw him collect another Ballon D’or crown early this year, after helping Madrid recapture a long awaited Champions League title last season.

After he set his sights on the Bernabeu, it was widely accepted that United would lose the Portuguese star at some point – something nobody held against him after all he had done for the club. But in a side that’s lacking a spark, Ronaldo and his magic on the ball is sorely missed at Old Trafford.