Manchester United completed the 20 million euro signing of Argentina World Cup defender Marcos Rojo from Sporting Lisbon on Wednesday with Old Trafford boss Louis van Gaal hailing the 24-year-old as a "gifted" player.
Rojo signed a five-year contract after impressing during the World Cup where he helped Argentina to reach the final.
Winger Nani has gone in the other direction, rejoining Sporting on a season-long loan, seven years after he left the Portuguese club.
"It is such an honour to say that I now play for Manchester United. The Premier League is the most exciting league in the world and to have the chance to play in it for the world's biggest club is a dream for me," said Rojo.
"I am young and am very keen to continue to learn the game, so playing for such an experienced technical coach as Louis van Gaal is a fantastic opportunity for me. I have joined United to work hard with my team-mates to win trophies and I know that the manager shares that ambition."
Rojo, who started his career with Estudiantes de la Plata, spent the past two seasons at Sporting having joined from Spartak Moscow in July 2012.
"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," said Van Gaal.
"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."
Rojo has won 28 caps for Argentina and will bring much-needed versatility to United's backline.
He becomes the club's latest major signing of the Van Gaal era after Ander Herrera and Luke Shaw and will be a crucial part of the Old Trafford jigsaw after United lost centre-backs Rio Ferdinand and Nemanja Vidic alongside left-back Patrice Evra in the summer.
United's defensive shortcomings were brutally highlighted at the weekend when they lost their season opener 2-1 to Swansea at the weekend.
The 27-year-old Nani made 228 appearances in all competitions for United, scoring 40 goals.
Meanwhile, Belgian midfielder Marouane Fellaini looks set to be sidelined after sustaining an injury in training.
United have not commented on the extent of the injury, but pictures in The Sun on Wednesday showed the 26-year-old on crutches with his left foot in a protective cast.