It has not been a good season at Manchester United, to say the very least.

Having shown promise but failed to find consistency during Louis van Gaal's first season at the Old Trafford helm, many expected the Red Devils to push for the Premier League title this year - especially after it became clear around October time that Chelsea wouldn't be able to retain the crown.

But with just twelve fixtures remaining, United aren't even on track to claim a Champions League spot, finding themselves six points behind fourth-placed Manchester City and twelve points away from the Premier League's summit.

It seems inevitable Louis van Gaal will be relieved of his duties before the start of next season, with Jose Mourinho the likeliest candidate to replace him. But the quality of player is arguably as big an issue as the man in the dugout - despite spending around £250million during the last two summer transfer windows, United's squad is short of world-class personnel.

But we know the Old Trafford outfit still have a considerable fortune to spend and we know they're going to spend it at the end of the season. With that in mind, here are FIVE world-class summer signings that would transform the 13-time champions back into title contenders once again...

MATS HUMMELS

Hummels

I know. We've been here before.

For pretty much every summer of his Dortmund career, Mats Hummels has been linked with a move to Manchester United and we're still waiting for it to actually materialise.

But the Red Devils still need a left-sided centre-back, a ball-playing centre-back and a world-class centre-back and the 27-year-old encompasses all of those requisites, as a former World Cup winner famed for his Beckenbauer-esque ability to instigate attacks from the heart of defence.

Furthermore and perhaps most importantly, the German international's Dortmund contract will enter its final twelve months come the summer which, provided their offered a healthy sum, could convince the Bundesliga outfit to sell. It certainly improves United's chances of signing him compared to recent summers.

RIYAD MAHREZ

Riyad Mahrez (centre)

Whilst the majority of Leicester City's players have performed far beyond their means this season, Riyad Mahrez's class appears to be of the permanent variety.

Indeed, the likes of Arsenal and Barcelona were reportedly throwing the Algerian international flirtatious glances last summer and he's since emerged as one of the most potent attacking forces in the Premier League, notching up 14 goals and 10 assists in 25 appearances.

There's an elegance and skill to Mahrez' game that suggests he could ply his trade at the very top level and now 24 years of age, the timing is right to take the next step in his career.

Manchester United are in desperate need of added and particularly speedy options out wide. Mahrez certainly fits the bill but you'd fancy Leicester's chances of keeping hold of him if they claim this season's title.

PAUL POGBA

Olympique Lyonnais v Juventus - UEFA Europa League Quarter Final First Leg

Could the Red Devils pull it off? Well, Paul Pogba must feel like he's got unfinished business at Old Trafford, making just three Premier League appearances before joining Juventus on a free transfer in summer 2012.

Despite being often overlooked by Sir Alex Ferguson, he's since emerged as one of the top midfielders in world football, combining a rangy and imposing 6 foot 2 frame with technical trickery and a consistent supply of goals - notching up 25 in 115 Serie A appearances for the Old Lady.

The France international resisted the temptation to leave last summer despite virtually every major European club courting his services but may feel a little different this time around. He's won everything there is to win at Juve apart from the Champions League title and the Old Lady seem likely to claim it any time soon.

No doubt, landing the 22-year-old would transform United and represent an enormous statement of intent. But the Red Devils will stand no chance of signing him without Champions League football, considering Barcelona, Real Madrid and Bayern Munich will all be vying for his signature once again at the end of the season.

ZLATAN IBRAHIMOVIC

Paris St Germain v Chelsea - UEFA Champions League Second Round First Leg

Zlatan Ibrahimovic may be 34 years of age but he's still one of the best in the business, notching up 28 goals across all competitions this term to bring his PSG tally to 134 in 162 outings.

Of course, we're all well aware of how talented the enigmatic Swede is, combining the 6 foot 5 frame of an old-fashioned target man with the technical skill of Dennis Bergkamp. He's not lost a title race since the 2002/03 season and will probably be remembered as the greatest striker of his generation.

Admittedly, the 111-cap international doesn't offer Manchester United much longevity and his potential wages would be humungous. But Zlatan's contract is due to expire at the end of the season and on a free transfer he'd be an absolute steal - even if his Old Trafford career spans just one or two campaigns.

But Ibrahimovich has been allowed to discuss pre-contract terms with foreign clubs since January 1st and something tells me he's already decided on his next team.

NEYMAR

NeymarBARCA

The tabloids seem to think ongoing tax troubles will push Neymar to the Premier League this summer, with Manchester City and Manchester United set to duke it out for the Barcelona star's signature.

The potential move would make sense for the Brazil international's career ambitions too. He's already claimed the Champions League title with Barca but the Ballon d'Or will likely ever-evade him whilst playing in the same line-up as four-time winner Lionel Messi.

Without question, the world-class talent would drastically improve the quality of United's attack. He's bagged 17 goals and eight assists in 20 La Liga appearances this season and produced a level of form unrivalled throughout world football when Messi was sidelined earlier in the campaign.

United are more than prepared to stump up the 24-year-old's £145million release clause in a bid to make him the 'poster boy' of the post-Ferguson era. Once again, however, the Red Devils will need Champions League football at the very minimum to convince Neymar into an Old Trafford switch.