The Red Devils went into last term as champions, but with David Moyes in place of the retired Sir Alex Ferguson, their defence of the trophy was an inconsistent one and the team eventually finished seventh.
However, Moyes's successor Van Gaal, who has won titles in Holland, Spain and Germany, has proven to Wenger at the World Cup in charge of the Netherlands that he has the credentials to return United to the higher echelons of the table.
"He is going to be a fantastic manager in the Premier League," Wenger told beIN Sports. "I liked how the decisions he made were clear [at the World Cup], how the timing of his decisions were always right and in my opinion it was the right decision every time.
"I am sure that Manchester United will be competitors this year for the championship and that will be more interesting."
Van Gaal is expected to arrive in Manchester early next week, before he travels to the USA with the squad for their pre-season tour.