When Belgium take on Portugal in the Round of 16 at UEFA Euro 2020 on Sunday, it will be the first-ever meeting between the two teams at a major competition.The high-scoring sides had contrasting fortunes in the group stage. Belgium won all their three games, keeping a clean sheet in two. Meanwhile, Portugal won only one of their three games to qualify as one of four best third-placed teams.See you in Seville, @selecaoportugal. 👋 #DEVILTIME #EURO2020 pic.twitter.com/jAkeG9PlB6— Belgian Red Devils (@BelRedDevils) June 23, 2021The reigning champions will have their hands full against a rampant Belgium. Portugal will need other players to complement the efforts of Cristiano Ronaldo, who has notched up five goals and an assist in the tournament.Both Belgium and Portugal have some of the world's best players in virtually all positions in the field. Many of whom have won league titles with their clubs last season. So the team that wins this game will fancy their chances of going all the way at Euro 2020.With the stage all set for the No.1 team in the FIFA rankings to take on the holders at the Estadio La Cartuja de Sevilla, let's take a look at five players who could be key in the outcome of the game.#5 Thomas Meunier (Belgium)Thomas Meunier has been excellent going forward.Wing-backs have assumed greater significance in the game in recent times. In the ongoing Euro 2020 tournament, many teams have played with two wing-backs in their lineup, one of these teams being Belgium.Roberto Martinez would've preferred to have Leicester City's Timothy Castagne starting against Portugal. But an eye injury has ruled Castagne out of the competition, meaning Borussia Dortmund's flying right-back Thomas Meunier will start in his place.4 - Thomas Meunier has been involved in four goals in his last five games in major tournaments with Belgium (2 goals, 2 assists). Spotlight. #BELRUS #EURO2020 @BlackYellow pic.twitter.com/9FVbSD2a4T— OptaFranz (@OptaFranz) June 12, 2021The 29-year-old has made a name for himself as a goalscoring defender. He has already opened his account in the competition, scoring and assisting in Belgium's Euro 2020 opener against Russia.His pace and ability to get into dangerous positions from the flanks is a welcome addition to Belgium's formidable attack. He will likely be up against club teammate Raphael Guerrero on the right flank. The Portugal defender's penchant to over-commit in attack is something Meunier would look to exploit.#4 Romelu Lukaku (Belgium)Romelu Lukaku is in great form at Euro 2020.There are a lot of players who have the ability to single-handedly change the outcome of games for Belgium. But the player who usually ends up finding the back of the net for the Red Devils is their striker Romelu Lukaku. He is expected to be the dangerman Portugal need to watch out for.The Inter Milan striker has continued his goalscoring form with Belgium, scoring three goals at Euro 2020. His physical strength, pace and tenacity in the box make it incredibly difficult for opposition players to defend against him.Two games played. Two Star of the Match awards.Romelu Lukaku is on a different level right now 👏 pic.twitter.com/pLNMvxgPPJ— ESPN FC (@ESPNFC) June 17, 2021Apart from his direct goal involvement, Lukaku is much more than just a target man. That was evident in his performance against Denmark, where Lukaku was key in the buildup of both goals in Belgium's come-from-behind win.Also Read: Netherlands vs Czech Republic prediction, preview, team news, and more | UEFA Euro 2020.