Manchester United boss Erik ten Hag says they must be "100 per cent" switched on at West Ham.
United's top four status is under threat from West Ham.
Ten Hag said: We have to keep our heads clear but also I demand passion from my players.
But I am telling the players that if you want to be in four competitions, you need so much energy and a good game plan.
You can't do it at 99 per cent, it has to be 100 and for 95 minutes. We like it but it costs energy. That's our job and Sunday we go again."