England begin their Euro 2020 campaign with a high-octane Group D clash against Croatia at the Wembley Stadium in London.Harry Kane and co. were knocked out of the 2018 FIFA World Cup in Russia by the same opposition in the semi-finals. So there will be added incentive for the Three Lions to get one over the Croatians.Another day done 💪The countdown to Croatia continues! pic.twitter.com/sD0SGBrFbv— England (@England) June 10, 2021Croatia themselves will be desperate to begin their Euro 2020 campaign with a victory, as they haven't had a decent stretch of wins in quite some time now. Although they will fancy themselves a lot more against relatively easy opposition in the matches to come, a positive result against England in the Euro 2020 tournament opener would be a massive morale-booster.Also Read: Fabrizio Romano's Transfer Roundup: Update on Manchester United's pursuit of Jadon Sancho, Chelsea's plans for Hakimi, and more.On that note, let's have a look at five players who could be key in the outcome of this game.#5 John Stones (England)John Stones is back playing for EnglandWhat a turnaround it has been for John Stones! Axed from the England team after a string of lacklustre performances for Manchester City, the 27-year-old defender has roared back to form this season.Most people had written off the former Everton man, and his Manchester City career seemed all but over. However, Stones never stopped believing in his abilities and chose to fight for his place. As things stand, he is England's best defender at Euro 2020, and there will be a lot of responsibility on his shoulders.📊| John Stones in 2020/21:👕 35 Apps⚽️ 5 Goals Scored🔴 16 Goals Conceded🚫 22 Clean SheetsNo player in 𝙀𝙪𝙧𝙤𝙥𝙚 had a better defensive record! 👏🧱 pic.twitter.com/ktdcfrZQNx— City Chief (@City_Chief) June 3, 2021Especially in the absence of his usual partner Harry Maguire, Stones will have to step up and marshall his troops well against a Croatia team that has plenty of good ball-playing players.#4 Bruno Petkovic (Croatia)Bruno Petkovic played a key role as Dinamo Zagreb knocked out Tottenham Hotspur in the Europa League.Expected to start up front for Zlatko Dalic's men, Dinamo Zagreb forward Bruno Petkovic will have a key role to play for Croatia at Euro 2020.The 26-year-old has scored 14 goals for his club across all competitions this season. However, it is his playing style that makes him key for club and country. He is a no. 9 who loves to involve his fellow offensive players in attack and isn't just a regulation goalscorer.Petkovic uses his strength to good effect and is good in hold-up plays. His partner up front - Ante Rebic - will likely benefit from the same. Petkovic is central to the way Croatia play in the final third.Their midfield is up there with the very best in the international arena. So there is unlikely to be any dearth of service for their forwards. If Petkovic is at his best, he could give England plenty of problems.Also Read: Arsenal contact Manchester United over a potential deal for midfielder - Reports.