Radamel Falcao has failed to reproduce his goalscoring heroics from Atlético Madrid. Photograph: Martin Rickett/PA

The concerns led United to take Falcao on loan from Monaco rather than buy him as Welbeck joined Arsène Wenger’s side for £16m, the same cost of the Colombian’s loan and wages for this season.

While Welbeck is enjoying a fine campaign, having scored 10 goals for Arsenal and England playing in his preferred centre-forward position, Falcao’s start to his United career has featured disappointing form and been hampered by injury.

The striker has scored once and was dropped by Van Gaal for the 2-2 draw at West Bromwich Albion before suffering the calf problem in training which will rule him out until early December.

Despite this, Van Gaal hopes Falcao will ultimately make the decision to bring him to Old Trafford pay off. “I hope so. That is clear, I think.

“But do you think that we expected he would be so many weeks injured,” he said, before admitting the cruciate injury of last season was a factor in the loan, hinting that a permanent deal could have been seen as too much of a gamble. “Yes, but because of that [injury] maybe we didn’t buy him and we’ve said that already.”

Van Gaal takes United to Arsenal for Saturday’s late kick-off insisting he has no regrets in allowing Welbeck, who should line up against his team, to leave.

“For him I have already explained, it was a very good decision because as a lineup player [a starter for Arsenal] he develops himself much more. And if it was the right decision for Manchester United, it’s dependent on how we play and we score and in what position we shall finish in the league,” said the manager.

“But after that you cannot say it is a very good decision or not because we are in another process to Arsenal. They have a manager who has been there 18 years and the playing style is 18 years the same. So that is very different. Here Danny Welbeck doesn’t play every match, mostly he doesn’t play.”

With Falcao, 28, Wayne Rooney, 29, and Robin van Persie 31, some argue that to allow the 23-year-old Welbeck to leave was short-term thinking. Van Gaal, though, pointed to James Wilson, who is 18.

“Wilson is a very good striker. He has to compete with these guys and it’s always difficult but when he wins this battle then he is a lineup player,” he said. “It is too easy to say something [have an opinion]. You are saying for weeks and weeks that we have a bad defence. Have you seen the goal average for Arsenal and the goal average for United? That you have to see and then you know the answer.”

Pressed how he had made the decision regarding Welbeck, considering he was never given a full season at United as a striker, the manager said: “I have already said what I think – he was not a lineup player, he was more a substitute than a lineup player and he was already with different coaches not a lineup player and then with Mr Van Gaal the world is changing?

“No, the world is not changing. They are the facts. They are not my facts, they are the facts of Danny Welbeck and we have Van Persie and we had Wilson and when you keep Welbeck then you don’t give any chance to youngsters and that is also our philosophy.

“And then also we could buy Falcao. When that is not enough reason then I don’t know what is – then I’m not a very good manager.”

With Van Gaal now favouring a lone forward system he warned that Falcao faces a fight to regain a starting berth when fit again. “I have explained to my players, it’s not only a question of fitness but also you have to train with the group,” he said.

“Then you have to be better than the players who are on the list. I’ve said that before. Until now he didn’t train with the group so it’s out of the question for him to be on the bench.

“I don’t give any chance to players when they are not fit. Believe me, see my record. See the Dutch team, see all my expressions about fitness, you have to be fit. What’s your name? It doesn’t matter, you have to be fit.

“And now we have a lot of injuries. So they are not fit, I’m sorry. Then I have to manage with the other players. And we believe in these players. And we shall show it.”