Manchester United may find themselves above their two main divisional rivals - Arsenal and Manchester City - in the Premier League table following a 2-1 win over Watford on Saturday, but doubts still remain over their title credentials.

Indeed, the Red Devils' defensive efforts can't be faulted, conceding just nine goals in 13 games to produce the best defensive record in the division, but their struggles at the other end of the pitch could prove to be the Old Trafford outfit's ultimate undoing come the end of May.

The balance of the squad doesn't feel quite right, so if United wish to enter the second half of the season as undisputed title favourites - most notably rivalling the incredible quality and depth on show at Manchester City - it could require some recruitment in January transfer window.

Louis van Gaal seems keen enough to spend, having hinted so on a number of occasions in recent weeks, and with that in mind, here are FIVE January signings that would make his side title favourites...

MARCO REUS

Louis van Gaal wants a speedy winger and Borussia Dortmund's Marco Reus is one of the best and speediest around.

He's claimed 44 goals and 28 assists in 92 Bundesliga appearances for the Black-Yellows, including seven league strikes this season, and has affirmed his reputation as one of the most prolific attacking threats in Europe since arriving from Borussia Monchengladbach in summer 2012.

Blessed with fantastic technical quality, blistering speed and great intelligence, Reus has operated as a winger, a No.10 and as a centre-forward throughout his Westfalenstadion career and impressed in all positions - seemingly equally adept in the roles of scorer and provider.

He certainly fits Louis van Gaal's preferred mould of the 'multifunctional footballer' and he'd certainly add a new, more dynamic element to the Red Devils' attack.

But after signing a contract extension until 2020 in February, Dortmund are well aware that they can command top dollar for their flagship entity. A £40million to £50million sum feels like the right ball-park.

RICARDO RODRIGUEZ

Hot off the press this morning, Manchester United have been linked with Wolfsburg defender Ricardo Rodriguez - who would certainly fill Luke Shaw's almighty void at left-back.

Indeed, the Switzerland international is one of the best attacking full-backs on the continent, bagging twelve goals and 19 assists in 95 league outings since the start of the 2012/13 campaign - six months on from joining the Volkswagen Arena ranks as a teenager from FC Zurich.

He's become an integral part of the Wolfsburg starting Xi, this season averaging 2.1 tackles, 1.7 interceptions and 1.5 created chances per match, but at 23 years of age seems destined to test himself at a higher level at some point over the next few years.

In theory, he'd be a fantastic January addition. But tied down until 2019, Die Wolfe are only likely to sell for a ridiculous offer. Furthermore, Rodriguez's arrival would make the left-back situation rather complicated once Luke Shaw returns from injury.

SAIDO BERAHINO

West Bromwich Albion striker Saido Berahino may not be the finished article just yet, but his penetrative pace and poacher's instincts would certainly be of use to a Man United attack currently lacking both.

Indeed, the 22-year-old has quickly emerged as one of the most exciting young strikers in the Premier League since bursting onto the scene with a superb strike at Old Trafford in 2013, going on to bag 22 goals in 80 Premier League outings. He's also England's second-top leading goalscorer at U21 level, his haul of ten only bettered by Alan Shearer and Francis Jeffers.

Capable of playing out wide or centrally, Berahino would certainly enhance Louis van Gaal's attacking options. Likewise, he's young and versatile enough to be moulded into any kind of forward that suits United, although speed and netting prowess remain his natural strengths.

Furthermore, the Burundi-born striker's intentions to leave the Hawthorns are no great secret. He came close to leaving in the summer, heralding his Twitter fiasco with chairman Jeremy Peace, and is currently stalling on the Baggies' latest contract offer. However, the club have made it clear they expect between £20million and £30million for the prodigious forward.

SHKODRAN MUSTAFI

Although Manchester United's defensive record this season can't be faulted, there is still a feeling that the Old Trafford outfit need another option at the heart of defence to become the indisputable partner to Chris Smalling.

He may not exactly address the limited experience in United's backline at the tender age of 23, but it's hard to look past Valencia's Shkodran Mustafi in that regard, having been amongst Europe's most in-form centre-halves since the start of the season.

Indeed, the one-time Everton youngster has averaged 2 tackles, 4.5 interceptions, 5.2 clearances and 2.7 successful aerial duels per match at the Mestalla this season, whilst bagging two goals in ten appearances.

Also a member of Germany's World Cup-winning squad in Brazil, Mustafi's huge potential has been noted by Die Mannschaft boss Joachim Lowe for some time.

He seems destined for the top but Valencia would expect an enormous return on the €8million investment made two summers ago if they're to sell in the coming transfer window.

MICHY BATSHUAYI

Another potential addition to Manchester United's striking woes. Marseille's Michy Batshuayi has become one of the stories of the season in Ligue 1, bagging nine goals and four assists in 14 outings, leading to a wave of speculation regarding a January move to England.

Indeed, Belgium internationals have taken the Premier League by storm over the last few years and the 22-year-old appears the next in line to do so, boasting power, pace, leap and netting prowess in seemingly equal measure.

Admittedly, it remains to be seen whether the 6 foot forward is the real deal or simply enjoying a sudden blaze in form. But his 39 goals in 97 outings for Standard Liege suggests the former scenario and having already been valued at £35million by Marseille chairman Vincent Labrune, his price-tag seems more likely to go up than down over the next few years.

It could save United immeasurable sums in the long-run to sign Batshuayi now. But a host of clubs, not least including Arsenal, Spurs and Newcastle, are believed to be tracking the Belgium prodigy.