Louis van Gaal believes Chris Smalling could be the next Manchester United captain. The manager has been impressed by the defender’s willingness to take instructions and lead the side by making his voice heard.

On Sunday United play Manchester City at Old Trafford in the 170th derby. Twelve months ago Smalling was sent off when the clubs met at the Etihad Stadium on 2 November. The 25-year-old responded by focusing on his game and developing under Van Gaal to become a first choice in central defence.

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When the United manager was asked who the club’s future captain might be, he said: “Wayne Rooney is the captain and so you don’t have to worry and then Michael Carrick but when they are gone then Chris Smalling can do that. So I push him also in that situation. Every player makes the steps by himself to improve. I put him in the situation and I help him in the situation and I advise and the player can take it on board or not. It is his responsibility. He has done it by himself. There is a lot of advice.

“It is about how we defend as a team. Smalling is a part of that and I wanted him to speak. He also has the talent to speak. That makes him easy to coach. Because of that I made him a leader of the team. He has made steps and also in a tactical way.

“When you give instruction in terms of organisation you need someone to understand that. He is a structured person. He accepted it more quicker. David de Gea [the goalkeeper] has the best view and then the central defenders so I demand of my defenders that they speak. They need also an overview. I put him in that situation and then he can develop or not. It is his choice.”

Last year Van Gaal had to cope with a catalogue of injuries that had reached more than 40 before Christmas, in his first season at the club. This term the manager believes the issue has been addressed and he admits being responsible for working his players too hard.

“That was my fault. I was training them harder but they were not used to training like that,” Van Gaal said. “Because I am convinced you have to train now they are used to that step. I also let go players because of that and I bought new players. I think they are more used to my training sessions. You can see that with the new players. You can see which players are always injured.

“In my career I never had injuries like that [last year]. I have always preferred small squads. I think I have the smallest squad in the Premier League. You always have to train but with structure and not too hard.”

Van Gaal suggested he may buy another player – maybe in January – though he denied his squad is too small. “No it is not, otherwise I would have had a bigger squad,” he said. “I believe in smaller squads because you need perspective, otherwise the motivation is a doubt. Last season we had 24 players. I think 22 players and three goalkeepers is enough so I am still one short.”

United drew 1-1 at CSKA Moscow on Wednesday in their third Champions League Group B match. It means they have four points and are second and have qualification to the knockout phase in their hands.

With United third in the Premier League, Van Gaal believes it is possible to win the domestic league and the European Cup. “It is always possible,” he said. “I have done that [with Ajax]. But I also lost when we were champions in Germany in the Champions League final [with Bayern Munich]. It is harder these days. The Premier League is the most difficult league to win because of the high level of the teams. You cannot beat a team easily. Every team is a challenge. It is a rat race and then you have to play also in the European Cup. It is not so easy and that is why English teams over the last few years have not won the Champions League because of the difference in the leagues.”

Van Gaal believes the attrition of English football affects clubs and the national team, branding it “evil”. He said: “There is no winter break and I think that is the most evil thing of this culture. It is not good. It is not good for English football. It is not good for the clubs or the national team. I think you should change it. England haven’t won anything for how many years? Because all the players are exhausted at the end of the season.”