Wayne Rooney had better tread carefully as United boss Louis van Gaal plots the second phase of his Reds rebuilding work.

Even being a double-winning captain doesn't spare you if you cross swords with the Dutchman.

Mark Van Bommel’s December 2010 row with Van Gaal at Bayern Munich came just seven months after the Dutch pair had engineered the German club’s Bundesliga and Cup winning success plus a Champions League final appearance.

The spat, however, led to skipper Van Bommel’s shock exit to AC Milan in January 2011.

The pair had been thrown together when Bayern appointed Van Gaal as manager in 2009 and Van Bommel’s says it was a pot-holed road to silverware but the United boss has the credentials to revive Old Trafford’s glory years.

“2009 was Louis’s first year at Bayern. It was a successful year. We won the Bundesliga, the cup and were in the final of the Champions League,” recalls Van Bommel.

“But it was a big change for the club. We had had Jurgen Klinsmann in charge and then Van Gaal came and it was totally different. He wanted to change the whole club. It was a change of culture from the German to the Dutch. It was totally different and we had slight problems in the beginning but everything settled down then in October we were winning.

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“In Germany we had the same problems as United. It is a total 100 per cent change. Given the time he has good ideas how to play on the pitch. But he is not easy to work with.

"On the pitch he is good but outside it was a little bit difficult. Maybe that is the life of a coach because sometimes you have to make decisions that are not so nice.

“He has a way and he goes straight. He has a way and it is his way. He wanted to go straight. He doesn’t want to go right or to go left, only straight. Everybody knows what he wants.

“I had a little problem with him in 2010 in December. I was the captain of the team and I had to protect my players. Maybe I was a little bit 120 per cent doing that. I wanted to help the other guys.

"Maybe I could have settled down and let it go. But that is the way I am. That is my character and it was his character as well.”

Van Bommel was in the Bayern dressing room on the memorable day Van Gaal dropped his trousers and underpants to explain why he had made certain substitutions! His actions were done to prove he had the balls to make the hard decisions.

“He is different from other coaches. You have to get used to him and if you do it is simple. Have respect for him but don’t be scared.”

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Click through the gallery to see United's transfer targets in pictures.