The Argentina international defender joined the Red Devils from Sporting Lisbon on Wednesday and his new manager is convinced that he has a bright future in the game
United agreed a €20 million deal with Sporting Lisbon for Rojo on August 18 that saw out-of-favour winger Nani heading in the opposite direction on loan, with the club officially confirming the deal on Wednesday,
The 24-year-old becomes Van Gaal's third signing of the summer, following the arrivals of Ander Herrera and Luke Shaw, and the Dutchman is convinced that he will be a big player for United in the coming years.
He told the club's official website: "Marcos is a very gifted defender. He has played at the highest level in world football and can play either as a central defender or left-back.
"He has ability, physical strength and a willingness to learn that means he has a very bright future ahead of him. He had a very strong World Cup and has been playing in Europe for a couple of years now. He is a very good addition to the team."
United have also been linked with a big-money move for Real Madrid winger Angel Di Maria and Carlo Ancelotti suggested on Monday that no decision has been made over the Argentina international's future.