He has managed Barcelona and Bayern Munich - but Louis van Gaal says he is 'amazed' by how big Manchester United are.

The Dutchman has revealed he has been stunned by the size of the Old Trafford club ahead of their tour of the United States and added that he got a taste of things to come on their trip across the Atlantic last season.

More than 109,000 fans packed Michigan's Big House to see United take on Real Madrid and Van Gaal, who joined the club after leading the Netherlands to third place in the World Cup, admits he was taken aback.

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Louis Van Gaal had a solid first season at the club as he helped them back into the Champions League

Louis van Gaal, pictured with Memphis Depay, is reminded of United's global fanbase on a regular basis

'That was unbelievable,' he said.

'It was the first few days of my managership in Manchester and the way of the enthusiasm of our fans and the amount of numbers was unbelievable.

'We have played four or five games there (in the US) and there were 300,000 fans in two weeks.

'Of course (in Michigan) they were also watching Real Madrid but most of them were in red shirts. It's amazing.'

Van Gaal has witnessed life at the German giants and the La Liga champions but he thinks United is a different proposition - and says he gets a reminder of that on a regular basis.

'When I drive to the Aon training complex I think there are 100 people who want me to sign a shirt or a photograph and most of these are from Asia,' he explained.

'It is unbelievable how popular Manchester United is.'

The Dutchman completed the signing of Depay from PSV Eindhoven for £25m last week

United will take on Barcelona in the US and Van Gaal is looking forward to a reunion with old friends from the Nou Camp.

'I have to say they play still with players I have coached but that's nice,' he said.

'Also a lot of the staff is remaining there. I think it is nice to see those people again.'

United, who will be based in Seattle and San Francisco, will also play Club America, Paris St Germain and San Jose Earthquakes.

But Van Gaal knows which game is the most important.