Catch us if you can: Manchester City are favourites to retain their Premier League title

London (AFP) - The Premier League roars back into action on Friday after another frenetic summer of transfer spending in the richest league in the world.

Champions Manchester City are favourites to become the first side in a decade to retain the title. However, hopes are high that Liverpool can end a near three-decade wait to win the league.

Chaotic off-seasons for Manchester United and Chelsea could undermine their challenge, while there is an air of optimism for a new era at Arsenal.

Here, AFP Sport looks at five things to look out for in the Premier League this season.

Third-season syndrome for Mourinho

Frustrated figure: Manchester United boss Jose Mourinho has endured an unhappy pre-season

Manchester United manager Jose Mourinho has cut a frustrated figure throughout pre-season, consistently lashing out at a lack of signings.

Tension between the Portuguese and a number of key players is also simmering. Mourinho has publicly criticised captain Antonio Valencia and Anthony Martial, while his relationship with Paul Pogba remains frosty after dropping one of the heroes of France’s World Cup win repeatedly last season.

Rising tension with the club’s hierarchy and his squad before the season even begins is eerily reminiscent of Mourinho’s disastrous third seasons in both his second spell at Chelsea and his stint with Real Madrid.

In those campaigns Mourinho lost his job having won the league the season before. At United he isn’t even starting from that position of strength having failed to win a trophy last year.

As fiercest rivals City and Liverpool strengthen for an anticipated shootout for the title, the ingredients are in place for another Mourinho meltdown at Old Trafford.

City still the benchmark

Serial winners: Manchester City added the Community Shield to Premier League and League Cup trophies won under Pep Guardiola

Champions City remain the team to beat after smashing a litany of records in romping to the title.

Unlike Pep Guardiola’s first two summers in charge, City haven’t blown the competition out of the water financially, although they have increased their attacking options with Riyad Mahrez for a club-record £60 million ($77 million) fee.

But they haven’t needed to after assembling a huge amount of young talent in recent years.

Even more will be expected of the likes of Bernardo Silva and Gabriel Jesus this season, while Benjamin Mendy’s return from a long-term knee injury solves City’s one issue last season at left-back.

Will Sarri be given time?

Maurizio Sarri has been handed little time to impose his style on Chelsea

Chelsea are playing catch up from the off after delaying their move to sack Antonio Conte and hire Maurizio Sarri until four weeks before the start of the season.

Sarri moulded Napoli into one of the most attractive sides to watch in Europe in three seasons, earning rave reviews from City boss Guardiola in particular.

However, his high pressing and slick passing style requires a lot of work on the training ground. With many of Chelsea’s key players only returning to training this week after their World Cup exertions, the Italian hasn’t been afforded much time to impose his ideas.

Chelsea’s lack of forward planning was also evident in a late rush for a replacement for goalkeeper Thibaut Courtois, who left for Real Madrid on Wednesday. The giant Belgian’s successor, Kepa Arrizabalaga, will be the most expensive goalkeeper ever once he completes a £71-million move from Athletic Bilbao.

Sarri should be able to call upon Eden Hazard, Willian and N’Golo Kante despite speculation over their futures at Stamford Bridge.

New era for Arsenal

Unai Emery has big shoes to fill as Arsene Wenger's successor after 22 years in charge at Arsenal

In contrast, Unai Emery was swiftly sworn in as Arsene Wenger’s successor at the Emirates and has clearly targeted building from the back as his first priority to get the Gunners back in contention for the top four.

The recruitment of goalkeeper Bernd Leno, experienced defenders Sokratis Papastathopoulos and Stephan Lichtsteiner and tough-tackling Uruguayan midfielder Lucas Torreira should provide a stiffer backbone.

And there is plenty to be excited about going forward with Pierre-Emerick Aubameyang, Henrikh Mkhitaryan, Mesut Ozil and Alexandre Lacazette united for a full season for the first time.

Emery has been handed a baptism of fire with City and Chelsea in his first two games in charge.

However, there is the possibility for a fast start with Arsenal far less affected by late returns to pre-season from the World Cup than their competitors in the top six.

No limits for newcomers

Lofty ambitions: Wolves have signed Portugal goalkeeper Rui Patricio

The ambition for most newly-promoted sides is simply to retain their Premier League status, but Wolves and Fulham’s moves in the transfer market suggest they are aiming for a top-half finish on their returns to the top flight.

Wolves have again utilised their close connections to super agent Jorge Mendes to snap up experienced Portuguese internationals Rui Patricio and Joao Moutinho.

Fulham beat off stiff competition for Ivorian midfielder Jean Michael Seri and have also spent big on making Aleksandr Mitrovic’s loan move from Newcastle permanent and Alfie Mawson, as well as a loan move for German international Andre Schuerrle.