Liverpool manager Arne Slot is anticipating a different challenge when his side face Manchester United for the second time in a month.The sides met in a pre-season friendly in South Carolina at the beginning of August, where the Reds earned a 3-0 victory over United.The bitter rivals clash again in their third match of the Premier League campaign and Slot is expecting a completely different atmosphere at Old Trafford on Sunday.Slot said: "It's going to be different, when we played them in the States I think it was 50-50 because of the fans."The atmosphere will be completely different because I'm not expecting half of the stadium cheering for us or that they are favour for us."That's going to be different, but what makes it more different is both teams have a lot of different players on the pitch."So you can't compare that game with the game on Sunday."Slot has overseen two straight victories over Ipswich and Brentford, but they now face a tough task on Sunday.Slot has taken charge of clashes between fierce rivals in the past, overseeing Feyenoord's meetings with Ajax during his time in Rotterdam, and he knows the importance of games against United ahead of his first trip to Old Trafford as Liverpool boss."If you start to work at Liverpool, everyone who comes in knows how important the game against United is," Slot said."It's similar to when you work at Feyenoord how big the game against Ajax is."People tell you, but it's not really necessary because if you follow the game of football, which I do for a long time, you know the importance of Liverpool against United."One of the most important things is preparing (players) for what they can expect."What they can expect is mostly about the players they face, but I think now