In one of the most fierce modern-day club rivalries, Manchester United and Liverpool will square off at Old Trafford in the English Premier League on Sunday.The hosts have kicked off their 2021-22 campaign on a great note, winning four of their first five league games. But they are winless in their last three, losing twice and drawing once. Though United did record a comeback 3-2 win over Atalanta in the Champions League, they will have their task cut out against Liverpool.The Reds are the only unbeaten team in the English top flight in the 2021-22 campaign. They are also the highest-scoring side in the league. After consecutive draws, they returned to winning ways with a 5-0 win over Watford in their last game.Liverpool FC@LFCAn unforgettable away success against this weekend's opponents 🤩Enjoy a look back at our 4-1 win at Old Trafford from 2009 👌4:33 AM · Oct 23, 20217235864An unforgettable away success against this weekend's opponents 🤩Enjoy a look back at our 4-1 win at Old Trafford from 2009 👌 https://t.co/6rydBGQAQSPassion and fervour will not be in short supply when the two old rivals meet on Sunday. On that note, here's a look at how the two Premier League powerhouses would stack up in a hypothetical combined XI: A 4-1-2-3 formation has been considered.Goalkeeper: Alisson Becker (Liverpool)Alisson has put in consistent performances between the sticks for Liverpool.David De Gea was at one point one of the greatest goalkeepers in the world. But on current form, the nod goes to Liverpool custodian Alisson Becker.He has been highly consistent for The Reds, helping them to a Premier League and Champions League title. This season, he has kept four clean sheets; three of the six goals he has conceded were against Chelsea and Manchester City.B/R Football@brfootballAlisson against Atletico:1:40 AM · Oct 20, 2021154101316Alisson against Atletico: https://t.co/m7qayQFcyiWhile he might not be the best goalkeeper with his feet, he is very solid when it comes to making reflex saves. Alisson also has a great sense of positioning when dealing with crosses.Left-back: Luke Shaw (Manchester United)Luke Shaw has impressed with his pace and work rate this season.Luke Shaw has come a long way from what was seemingly a career-ending injury in 2015. The left-back's impressive performances for Manchester United earned him a place in the national team.His pace and penchant to link up with attackers in the final third makes him a very dangerous opponent to go up against on the flanks. He has only one assist to his name this season.Shaw's attacking output could be limited in this game, though. That's because he will have to put in a great shift defensively against Liverpool's in-form attacking trio of Mohamed Salah, Sadio Mane and Roberto Firmino.