Manchester United boss Louis van Gaal has warned his players that Champions League qualification is still not assured despite holding an eight-point gap over Liverpool after Saturday's results. Following a comprehensive 3-1 victory against Aston Villa, Van Gaal sees next Sunday's derby against Manchester City at Old Trafford as important in the battle to finish runners-up. But having been given the task of qualifying for the top-four when he replaced David Moyes last summer, he is not letting complacency risk success, though Liverpool's 4-1 defeat against Arsenal on Satuday lunchtime puts United firmly in pole position. Ander Herrera celebrates with team-mates after scoring his team's third goal at Old Trafford . 'It is not done yet,' he said. 'We still have to play everyone else in the top four and the table shows they are the best teams. 'Of course we have a big gap and can afford to suffer a defeat but everything is possible.' However, van Gaal also sees the derby as an opportunity to push United's claims for a top-two finish. ‘I am looking higher up. The derby is a game for the higher places. Chelsea are likely to be champions but you have to keep on putting pressure. Spanish duo Juan Mata and Herrera celebrate the win against Aston Villa at Old Trafford on Saturday . Manchester United's Wayne Rooney celebrates with team-mates after scoring his team's second goal . ‘Manchester City, is a different game to this one against Villa. City shall not come with such a defensive strategy. We have seen the same with Tottenham and Liverpool. These are the matches wehre you can see fantastic matches. There may even be a shock recall for £60million man Di Maria who has been used as a substitute in recent weeks. 'His turn is coming, that I know. But he has to wait for the right moment,' said van Gaal. Angel di Maria has been used as a sub in recent weeks but he is closing in on a return to the starting line-up . Rooney battles with Aston Villa ace Jores Okore during Saturday's victory at Old Trafford .
Manchester United beat Aston Villa to secure an eight-point cushion .
Louis van Gaal's side currently sit third a point ahead of Manchester City .
Rivals Liverpool find themselves in fifth following their defeat to Arsenal .
But Van Gaal has warned his squad it is important to battle till the end .