Louis van Gaal has expressed his surprise at José Mourinho’s sacking by Chelsea and admitted it could be “the end of the world” for him as well if Manchester United’s results do not improve.

United are without a win in their past five games in all competitions and were knocked out of the Champions League last week. They have scored only four times during this time, their last victory coming at Watford on 21 November.

Van Gaal is conscious that while he retains the backing of the executive, all managers live or die by results. “I have the full confidence of my board and my players, that is what I feel,” he said. “But we have to get results, we have to win. We know that, the players know that, I know that and the members of staff know that. There is no doubt that we have to win because when you lose too much then even for me it is the end of the world.”

Of José Mourinho’s sacking, Van Gaal said: “What I can say, it was a big surprise for me, I didn’t expect that. A fantastic manager with a record that nobody has in this football world but it is still possible. What [is important is what] I’ve said last week: the main thing is always, of course, the results. Second, the chemistry between the players and manager and his staff. I cannot judge what was happening in Chelsea but I was very surprised.”

He said he knows no manager is safe. “It’s like that but we know that in advance. It’s this world. José knows that also.” Despite United’s uneven form, Van Gaal said team spirit is strong. “Yes it’s fine,” he said. “But I’ve said already more than once, I have seen articles that it’s not like that. It’s a bit crazy I think but that is this world.”

Wayne Rooney could return for Norwich City’s visit to Old Trafford on Saturday, having missed three matches because of a foot problem. If the captain features it will be his 500th appearance for United.

“It is possible that he shall play but we have to wait and see,” Van Gaal said. “[Ander] Herrera has trained a full week. But Herrera hasn’t played for four weeks, that’s different. Rooney hasn’t played for two weeks so it’s possible he can play. We have other players who have trained only one day then it’s too much risk normally but in these circumstances you have to take risks,” he added, in reference to the club’s long injury list. Chris Smalling has trained for a full week and is in contention too.

Talking about the need for a win over Norwich, Van Gaal said: “Every game has its own pressure, every week you have to do it in different circumstances. What is the same is the preparation, we always prepare very good the qualities of our opponents and our game plan. The players apply that and do their utmost best. We hope to give the result that everybody is expecting.”