Henrik Larsson
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He never seemed particularly interested in transfers unless he knew the players from before. Most of the players he really wanted were weak and/or bad fits and it didn't look like he had a real plan how to use them. He really seems to struggle to judge players before they trained and played under him for several months, which makes big transfers basically a huge gamble and it shows in his highly questionable transfer record. Robben is the only player we signed during van Gaal's time as Bayern manager who was still at the club 3 years after van Gaal left and Robben was pushed on him by the board because we panicked after a shockingly bad start. Van Gaal helped to make the deal happen in the end, but Robben wasn't really his signing in the first place.
It was just as bad if not worse during his time at Barca, where he just bought one Dutch player after the next one and alienated the fans with his signings, who mostly sucked when playing for the team.
Strange assesment. Robben is a Van Gaal signing. In every transfer there is a board involved, Bayern were a big club and the fact that he didn't want to go to Italy and had already played in England and Spain also played a part in the transfer. But I've literally heard Robben say that the fact that he personally knew van Gaal and had worked with him before (In Argentina, at the World Cup -21 in 2001) was vital for him coming to Bayern. But obviously Van Gaal didn't want him, because he didn't already know how good Robben was and he had loads of other world class options for the right wing.
I'd say what happened is this: the Bayern board brought in Gomez and Tymoschuk for 50+ million euro and Olic for almost nothing, then they signed Van Gaal. He brought in Pranjic, Braafheid and Robben for 40 million euro and won the Bundesliga, the cup and made it to a Champions League final. Without really using record signing Gomez and Tymoshuk, he played Schweinsteiger in midfield and Olic up front.
Second season Kroos came back from Leverkusen, Alaba was breaking through. Meaning he had Van Bommel, Schweinsteiger, Kroos, Tymoschuk as midfield options. Müller, Robben, Ribéry, Gomez, Olic as attacking options. Lahm, Alaba as (potentially) world class players in defense. The only thing that squad really needed to improve was a world class defender, but there aren't that many out there, and I don't know who was for sale that summer.
I think that was the biggest 'mistake' Bayern including Van Gaal made, because they also let Lucio go in 2009. With injuries I remember Tymoschuk eventually ending up as a CB and it looked laughable. But then again Badstuber looked like a prospect for CB with Alaba as a new LB option, so it wasn't that weird.
Bigger problem than the transfers in his 2nd season was the aftermath of World Cup 2010. The dramatic Robben injury that still remains a mystery today. Captain Van Bommel lost 30% of his skills and was on his last leggs, he had a fall out with Van Gaal and moved in the winter, he was replaced with Luis Gustavo. New players like Müller who just had their first full season and a World Cup after that. Together with Van Gaals general behaviour (he had some insane ego-trips in his time in Germany), that's the reason he was fired eventually.
Also in general, go and look at the 'Van Gaal's all time XI'. You can make 4 or 5 full squads with the best players imaginable,it's unbelievable how many superstars he's worked with. Go and read a little bit about his transfers at Ajax, or look at some of his AZ players (Dembele, Sergio Romero, Moreno, Moisander, Graziano Pelle). There's nothing to worry about, unless you are a drama queen.