Manchester United manager Louis van Gaal has admitted the derby against Manchester City on Sunday could be a “do or die” game for his club’s Champions League qualification hopes this season.

Van Gaal, though, fought back when asked if he was under pressure, pointing out that he has been linked with the sack for “four months.” The Dutchman admitted that United have fallen short of expectations this season but said that the circumstances need to be taken into consideration.

United were knocked out of the Europa League by Liverpool on Thursday, meaning that their only route into next season’s Champions League is by finishing in the top four of the Premier League. If sixth-placed United win the league match at fourth-placed Manchester City on Sunday then they will cut the gap behind Manuel Pellegrini’s team to just one point, while defeat would leave them seven adrift.

When asked if the game is “do or die,” Van Gaal said: “I think so. We are now four points behind so you have to win, otherwise the gap is bigger and bigger and the matches you have to play are not so many. If we lose, then it is seven points and we have eight matches left, so it is very sharp to recover from that gap. It is still possible but it’s difficult then, because West Ham United is also in front of us [in fifth place]. It’s not only City.”

Coming after such a damaging defeat against Liverpool, the City game is badly timed, but Van Gaal thinks that past form should not be taken into consideration.

He said: “Do you think that every game is the same game? Every game is different with different players, referees and circumstances.”

When Van Gaal’s job prospects were questioned, he started becoming more prickly.

The United manager addressed that on Thursday, saying: “I never feel that I am under pressure. I do what I have to do. Do you feel you are under pressure? What do I have to say now?”

He was questioned about whether his future in the job is dependent on qualifying for the Champions League.

“I don’t discuss that with you,” Van Gaal said. “Why do I have to discuss that? Every day when we lose, you put that question, but why? I have a three-year contract and the process is three years.

“When you are for four months writing — or your colleagues — that I shall be sacked, I have read that for four months already. You think that is logical, normal?”

It was pointed out that Van Gaal could be considered to have not lived up to expectations, but he retorted that “expectations can be too high.”

When asked what his expectations were, he said: “Our purpose was to reach the top three because we want to do better than last year — but, then, you have to analyse the circumstances, how I have to work.”

Some suggestions were put to him, regarding what the circumstances might be, such as injuries, but he refused to elaborate.

“You can fill that in. I have said these in all my press conferences,” Van Gaal said. “I don’t repeat myself any more. You are repeating, always putting me the same questions when I am losing.”

City will be without centre-back Vincent Kompany for at least a month after he suffered a calf problem during Tuesday’s 0-0 draw at home against Dynamo Kiev in the Champions League.

Kompany’s defensive colleague Nicolas Otamendi also went off with a leg injury in that match, meaning that City had to use a makeshift centre-back partnership in the second half of Martin Demichelis and Eliaquim Mangala. Otamendi, though, is hopeful of a swift recovery from his problem.

Van Gaal said: “We have to disorganise their defence. We know maybe Otamendi and Kompany cannot play. So they could play with Demichelis and Mangala.

“I will sit down with my staff and discuss the game plan. It depends also which players are fit to play because we have played [against Liverpool] a few days before City. You have to wait and see who is available. That also has an influence on my game plan. It’s not so easy to be a manager.

“Normally we play always in the same style and we try to press in a certain way, depending on the opponent’s quality.”

The United manager said that, having played against Liverpool, his team were being given a rest ahead of the derby on Sunday.

“Now the players are recovering, taking ice baths, so I cannot train in between.”

Press Association contributed to this report.