The 2018-19 pre-season has really taken off with the clubs going about their business in the transfer market. The Premier League clubs are at the epicentre of it all.Manchester City signed former Leicester City winger Riyad Mahrez for a club record €67 million and their fierce derby rivals Manchester United completed the signings of Fred and Diogo Dalot for €59 million and €22 million respectively.Merseyside club Liverpool FC made a host of signings in Naby Keita, Fabinho and Xherdan Shaqiri for €60 million, €50 million and €14.7 million respectively.London based clubs are not far behind as both Arsenal and Chelsea changed their managers and are trying to bring in fresh faces to the club. Arsenal with Unai Emery at the helm have considerably done great business on a low budget by bringing in the likes of Lucas Torreira, Bernd Leno and Sokratis Papastathopoulos for €30 million, €25 million, €16 million respectively while also bringing in veteran fullback, Stephan Lichtsteiner for free.Chelsea meanwhile announced Maurizio Sarri as their new manager while also bringing in Jorginho for a reported €57 million fee. Tottenham, on the other hand, haven't signed any new player this window.After the first round of business, we look at the key areas that each of the top 6 teams has to reinforce for the upcoming season.ArsenalEmery has big shoes to fillThe new Gunners boss was quick to act after being appointed Arsenal boss back in May and he has already signed a bunch of players for the North London club - Stephan Lichtsteiner, Sokratis, Bernd Leno, Matteo Guendouzi and Lucas Torreira.While these players will surely serve to upgrade the squad, there are still some grey areas that need to be reinforced before the window closes. Emery must be aware of this fact as more players are linked to the Emirates on a daily basis.Adding Sokratis to the defensive mix is a good move by the new Arsenal boss but the former Dortmund player is too heavy on the ball and needs a pacey centre-back to cover for him. Adding another experienced centre-back to his squad would help his backline.The Emirates outfit must also look to sign an attacking midfielder that would add to the creativity for Aubameyang and Lacazette to feed off.Players linked to Arsenal:Andre Gomes - FC BarcelonaNot the best period in the career of this Portuguese player, Gomes came to Barca as a world-class talent but failed to replicate his form from Valencia. Most of his problems started because of his inability to mentally prepare himself for the sheer weight of expectations from the club. A move to Arsenal is beneficial for both parties. Gomes could thrive in a 4-2-2-2 system playing in a double pivot alongside Xhaka or Torreira.Steven N'Zonzi - Sevilla FCA former Stoke City player and current Sevilla Starter is a tall and physical box to box midfielder, someone whose kind was missing from the Gunners squad for so many years.Ever Banega - Sevilla FCArgentina in this year's World Cup looked like an average team for most of the games. That was until Ever Banega came onto the pitch and balanced things out for La Albiceleste. His vision and passing ability put together with a fine defensive display almost entirely lifted the creative burden off Messi's shoulders. Add him to a midfield with the likes of Ozil, Mkhitaryan, Torreira and Xhaka and expect fireworks.