The race for the Premier League title is shaping up to be the tightest for some time with none of the 'big six' having stamped their authority on the competition during its early stages.

Here, the PA news agency takes a look as the issues facing the usual suspects as they attempt to slip into top gear.

Liverpool

Liverpool steamrolled their way to the title last season as miserly defence and clinical finishing laid waste to the opposition. Mohamed Salah and Sadio Mane – but not, as yet, Roberto Firmino – have already been back among the goals, but at the other end, a return of one clean sheet in six games in all competitions – one of them an eye-watering 7-2 drubbing at Aston Villa – tells its own story. Addressing that issue will be all the more difficult with central defender Virgil Van Dijk facing much of the season on the sidelines as he prepares to undergo knee surgery.

Manchester City

At their best, City are simply irresistible going forward with the brilliance of Kevin De Bruyne and the potency of Sergio Aguero and Raheem Sterling usually more than enough to blow away all but the very best. However, defensive frailty has been a theme for much of Pep Guardiola's reign to date despite heavy investment in reinforcements and those problems persist despite the £40million summer addition of Nathan Ake to the mix. Aymeric Laporte was missing for a shock 5-2 home defeat by Leicester, which featured a Jamie Vardy hat-trick, but was in the side as they failed to hold on to a 1-0 advantage at promoted Leeds.

Chelsea

The Gunners remain a work in progress under Mikel Arteta, who is just 10 months into his reign. Going forward, they remain a real threat with Eddie Nketiah complementing the firepower of Pierre-Emerick Aubameyang and Alexandre Lacazette. However, a defence in which the talented but error-prone David Luiz is a central figure continues to be a source of concern and the recruitment of Thomas Partey, a defensive midfielder whose physical presence and energy may prove as important as his ability to pick a pass, will provide an added layer of security.

Tottenham

During his time at Chelsea, Jose Mourinho built teams which were ruthlessly efficient, scoring enough goals to win comfortably without over-exerting themselves and keeping clean sheets into the bargain. Mourinho's Tottenham are in many senses the antithesis of that. In Harry Kane and Son Heung-min, they boast two of the Premier League's most potent frontmen, and the addition of the returning Gareth Bale will further boost the firepower at the manager's disposal. However, they have conceded in each of their nine games to date this season and at times have demonstrated a costly inability to kill off games, Newcastle snatching an undeserved draw in north London with a late penalty and West Ham fighting back to claim a point on Sunday despite trailing 3-0 after just 16 minutes.

Manchester United

It is not so very log ago that David De Gea was widely regarded as one of, if not the, best goalkeepers in the world and his subsequent difficulties have exposed the inadequacies of the men immediately ahead of him. Coupled with £80million central defender Harry Maguire's recent poor run of form – the England international turned in a much-improved display at Newcastle on Saturday evening – and the alarming fashion in which United capitulated in the wake of Anthony Martial's dismissal in the 6-1 rout by Tottenham at Old Trafford, the foundations have been less than firm. The class of Bruno Fernandes and Marcus Rashford will atone for some of those deficiencies, but that is not a blueprint for lasting success.