Since taking over at Old Trafford, Van Gaal has spent around £150m on players such as Angel di Maria and Radamel Falcao, but has been criticised for not reinforcing the Red Devils defence with experience.
Gullit believes that the United manager's choices in the transfer market suggest that he has misjudged the nature of Premier League football.
He told the Daily Mail: "How on earth is it possible that such an experienced and successful manager thought he could start the season at Man United without buying a couple of really strong central defenders?
"I am still amazed by his buying and his transfers. If you only strengthen the midfield and the attack, than you are underestimating the level and the power of the Premier League.
"If you want to survive in the top flight of English football you start with the foundation and you build the roof of your house last. Van Gaal has done it the other way round."
Manchester United returned to winning ways with a 2-1 win over West Ham United on Saturday.