Alexis Sánchez
Alexis Sánchez has been one of the biggest signings of the Premier League transfer window so far. Reuters

The World Cup may still be fresh in the memory but there is little time for reflection with the start of the Premier League season now exactly one month away. Last season was one of the most exciting ever, with managerial changes at most of the big clubs breeding much unpredictability as teams fought to take advantage of the power vacuum created by Manchester United’s dramatic decline.

There may not be quite so much upheaval this time around, but the post-World Cup excitement and some major new arrivals means there is much to look forward to. Here’s a recap of the already substantial transfer business undertaken by the five leading Premier League title contenders and what else they need to do to give themselves the best chance of lifting the trophy next May.

Manchester City
What they’ve done:
The champions have already addressed some key needs with Willy Caballero arriving from Malaga to provide a quality back up and possible competitor to goalkeeper Joe Hart and Fernando finally joining from Porto to give Manuel Pellegrini a natural holding midfielder to balance the more attacking instincts of Yaya Toure and Fernandinho. The free-transfer capture of Bacary Sagna was something of a surprise given that Pablo Zabaleta has been one of the Premier League’s best right-backs in recent seasons.

What they still need: Martin Demichelis was impressive at the climax of the season, but a club with Manchester City’s ambitions needs another top class option to join Vincent Kompany, especially with Matija Nastasic’s injury problems. It appears that City may decide to finally bite the bullet and stump up the £32 million to secure Porto’s highly rated France center-back Elliaquim Mangala. Ideally a leading left-back would also arrive.

Liverpool
What they’ve done:
Having achieved their primary objective of returning to the top four last season, Liverpool have moved quickly to reinforce their squad for the demands of the Champions League. Rickie Lambert offers a more physical, but still technically capable, option up front, while his former Southampton teammate Adam Lallana and exciting Serbian starlet Lazar Markovic offer different attacking options either out wide or through the middle. Emre Can has joined from Bayer Leverkusen to bolster the center of midfield.

What they still need: Much work still needs to be done if Liverpool are to match their second-placed finish last season as well as make progress in the Champions League. The departure of Luis Suárez has dramatically increased the money at Brendan Rodgers’ disposal but also presents him with a huge void to fill. It is likely to be filled by several players that Rodgers can mold rather than a ready-made superstar, but Liverpool are certainly in need of another quality striker. Still raw Belgian youngsters Romelu Lukaku and Divock Origi have been strongly linked. The defense also needs to be strengthened. Dejan Lovren could yet arrive from Southampton and would be a quality addition to the center of defense, while Alberto Moreno is likely to arrive to address a hole at left-back.

Chelsea
What they’ve done:
Having failed to secure a trophy in his first season back at Stamford Bridge, Jose Mourinho is clearly keen to ensure that there is no repeat in his second. Despite an awful World Cup, Diego Costa should fit seamlessly into Mourinho’s system and provide Chelsea with the presence up front they sorely lacked last term. Costa’s former Atletico Madrid teammate Filipe Luis will also give Chelsea an upgrade at left-back. The arrival of Cesc Fabregas is less clear cut. While clearly a fine player, it remains to be seen just where and how he will fit into a Mourinho disciplined team.

What they still need: Will Mourinho trust the attack-minded Fabregas to play in a central midfield duo? It seems unlikely, and if not a dynamic midfielder in the mold of Michael Essien in his prime should be sought to partner Nemanja Matic. Paul Pogba would be a dream signing, but may prove out of reach. With David Luiz departing, another center-back may be required, despite the arrival of highly rated French teenager Kurt Zouma. With Demba Ba on the verge of exiting and Romelu Lukaku and Fernando Torres potentially following, another striker could also be needed. A sensational return for Didier Drogba has been mooted.

Arsenal
What they’ve done:
Arsene Wenger predicted business would be slow due to the World Cup, but that only proved true once again for his club, as Arsenal’s rivals made decisive early moves. Then came a major statement of intent with the £30 million signing of one of the World Cup’s standout performers, Alexis Sánchez. Arsenal were desperately short of attacking options last season as well as, during the long injury absences of Theo Walcott and Aaron Ramsey, pace going forward. Sanchez addresses both of those needs and, for the second straight summer, provides the buzz of signing a ready-made star.

What they still need: A right-back is an obvious priority following the departure of Bacary Sagna. Newcastle United’s Mathieu Debuchy is thought to be on the verge of completing a transfer and should slot in seamlessly. In addition, Arsenal still badly need a real presence in the holding midfield role. While Wenger’s tactics left much to be desired, Mikel Arteta was badly exposed last season in heavy defeats to all of Arsenal’s rivals. Sami Khedira is a target and, though, not a natural holding midfielder, his quality, physicality, influence and winning mentality would make him a superb addition.

Manchester United
What they’ve done:
New manager Louis van Gaal means business and, despite a disastrous seventh-place finish last season, will target nothing less than the Premier League title in his first season. Despite being busy guiding the Netherlands to the World Cup semifinals, he has proved more decisive than his predecessor by green-lighting deals for impressive young left-back Luke Shaw and former Athletic Bilbao midfielder Ander Herrera.

What they still need: While David Moyes was always a misguided appointment, Manchester United also paid the price for a lack of investment in the squad in recent seasons. The champions of two seasons ago may have already spent close to £60 million, but much reinforcement is still required. Despite Herrera’s arrival, a dominant midfield presence is, as has been the case for five years, still required. Arturo Vidal is the perfect solution, but, with Juventus insisting they won’t sell, the Chilean could remain a fantasy for United fans. In addition, an established center-back is needed to replace the departed Nemanja Vidic and Rio Ferdinand, while another striker and a top class winger wouldn’t go amiss.

Verdict: Chelsea and Manchester City have each already addressed key needs and look set to further invest. Much time remains in this transfer window, but they currently appear best placed to battle it out for the title.