Manchester United’s early season optimism was dealt a significant blow on Sunday when Louis van Gaal’s side were humbled 3-0 at Arsenal. After topping the Premier League table, Van Gaal had talked of his ambition to win both the domestic championship and the Champions League title in this, his second season in charge. But the manner in which they were brushed aside at the Emirates Stadium proved there is still plenty of work to do to regain their once-mighty status.

Despite shelling out nearly £250 million since Van Gaal took the reins, it still won't be of much shock to the club's hierarchy that more needs to be spent. United have set their sights on some of the world’s top stars of late and still appear determined to make a real impact in the transfer market.

One of those it is believed they fruitlessly pursued in the summer was Barcelona’s Neymar. The Brazilian was part of a record-breaking forward trio alongside Lionel Messi and Luis Suarez last season, but is approaching the crucial stage in a player’s contract where he will have just two years remaining on his contract. There has apparently already been contact with Manchester United, although the move has been seen as a long-term ploy to get the 23-year-old to Old Trafford, potentially next summer.

And Neymar is thought to be considering the proposal. While he won a clean sweep of medals in his second season at Barcelona last term, there is a belief that he may be tempted to move out of the shadow of Messi at the Camp Nou and join another huge club where he would be the face of the organization. In an interview on Catalunya Radio this week, however, Barcelona director of football Robert Fernández insisted that Neymar would not be going anywhere.

“We're working on Neymar's new contract and I don't think there'll be any problems whatsoever,” he said, according to Spanish sports daily Marca. “I have no doubt that Neymar will spend the rest of his career at Barcelona.”

United are finding that, just because they have the money, signing the world’s outstanding players will be far from straightforward. The same message has been received during their pursuit of Thomas Müller. Stories emerged in Germany over the summer that United had offered 100 million euros (£74 million) for the forward, who has already scored 10 goals this season for Bayern Munich.

Speaking in recent days, Bayern chief executive Karl-Heinz Rummenigge has confirmed that there was contact from Old Trafford this summer, but insisted that they were wasting their time.

“I am not a banker,” he told Sport1. "We are a football club. That is why we never even considered selling Thomas Müller.

“I told my colleagues at Manchester United: 'I cannot close down my email account, but you no longer need to send me anything. It is useless.’”

One of the more obvious weaknesses currently in the Manchester United team is in defense. Already far from blessed with quality after failing to sign Sergio Ramos and Mats Hummels in the last transfer window, a serious injury to Luke Shaw has prompted a reshuffle that has further exposed the problems at the back.

Reinforcements could well be sought when the transfer window reopens in January. According to Portuguese publication O Jogo, one of those targeted could well be Bruno Martins Indi. It is claimed that Van Gaal has already sent scouts to watch the defender in action of late. Van Gaal should be well aware of Martins Indi’s abilities, however, having coached him during his time in charge of the Netherlands.

The 23-year-old may appeal due to the fact that he can play at either center-back or left-back. Yet it would be a major surprise were United to believe that Martins Indi were of the quality required to improve their defense.