The transfer market is slowly picking up pace. Now that the Euros and the Copa America are over, all the spotlight is back on how clubs can improve their squads. Manchester United have already signed Jadon Sancho in a big-money deal, while more such moves are expected. There could be heavy movement in the Premier League, with star players linked with moves away from their current club.Barcelona have already concluded the lion's share of their business, while little is expected from Real Madrid. Having said that, anything can happen during the summer transfer window, and it is always better to expect the unexpected.In this article, we look at 5 big transfers which could still happen this season.#5 Antoine Griezmann to Atletico Madrid FC Barcelona v Athletic Club - Supercopa de Espana FinalIt would be fair to say that Antoine Griezmann has never truly settled at Barcelona, and it is not surprising to see him linked with a move away.Griezmann was one of the best players in the world during his time with Atletico Madrid. He made 257 appearances in all competitions for Diego Simeone's men, scoring 133 goals and providing 50 assists. During this period, he also won the World Cup with France, and was one of his country's best players at the tournament.Barcelona and Atletico Madrid are close to agreeing a swap deal involving Antoine Griezmann and Saul Niguez, according to Cadena Cope ♻️Who's getting the better end of the deal? 🤔 pic.twitter.com/lJpD1NUfi8— Goal (@goal) July 14, 2021Barcelona signed him for £108 million in 2019, and are yet to see the best of him. The France international has made 99 appearances in all competitions, scoring 35 goals and providing 17 assists. He is one of the highest wage earners at the club, and given Barcelona's precarious financial situation, the forward is one of the players who looks likely to leave the club this summer.Atletico Madrid have been linked with him in a deal which will reportedly see midfielder Saul go to Barcelona. The Blaugrana have already strengthened their attack this summer with the additions of Memphis Depay and Sergio Aguero. The 30-year old Griezmann is said to be happy to return to his former club. #4 Erling Haaland to Chelsea Borussia Dortmund v Manchester City - UEFA Champions League Quarter Final 1: Leg TwoChelsea are after a striker this summer, with their incumbent choices failing to inspire confidence in manager Thomas Tuchel.Tuchel is clearly not a fan of Tammy Abraham, while Timo Werner's first season with the club was decidedly mixed. Veteran striker and able backup Olivier Giroud recently signed for AC Milan and it is evident that strengthening the attacking department is of primary importance for the Blues.Erling Haaland to Stadium Astro: “I talked a little bit with new manager Marco Rose. I know him from before because I had six months with him in Salzburg. He's a nice guy and I look forward to working with him”, @BVBBuzz reports. 🟡⚫️ #BVB #Haaland— Fabrizio Romano (@FabrizioRomano) July 17, 2021Signing one of the best young strikers in world football would be an instant solution to the problem. Chelsea are reportedly heavily interested in signing Borussia Dortmund's Erling Haaland this summer. The 20-year old is already a superstar. He has made 59 appearances in all competitions for the Bundesliga giants, scoring 57 goals and providing 15 assists.However, signing him this summer will not be easy. Borussia Dortmund have already sold Jadon Sancho to Manchester United, and it seems unlikely that they will sell another of their big names this time around. It has been suggested that Chelsea could include Abraham or Callum Hudson-Odoi in the deal in order to get their man.Also Read: Fabrizio Romano's Transfer Roundup: Update on Manchester United's transfer plans, Barca's plan for Antoine Griezmann and more