Former Barcelona goalkeeper Victor Valdes has signed for Manchester United as "the number two goalkeeper", said manager Louis van Gaal.
The 32-year-old Spain international has penned an 18-month deal, with the option of another year.
"I can already see this is a very special club," said Valdes, who will deputise for David De Gea.
"I worked with Louis van Gaal during my time at Barcelona and to have the opportunity to work with him here at Manchester United is a dream come true."
Van Gaal said that Valdes had been "very impressive" during training.
"He joins the club as the number two goalkeeper and is a great addition to the first team," the Dutchman added.
|Valdes's honours at Barcelona|
|La Liga: 2005, 2006, 2009, 2010, 2011, 2013. Copa del Rey: 2009, 2012. Champions League: 2006, 2009, 2011. World Club Cup: 2009, 2011.|
Valdes's arrival has caused some to question about the future of 24-year-old first-choice goalkeeper De Gea, who was the club's player of the year last season.
His contract is due to expire in 2016, although senior United sources have said they were relaxed about him signing an extension to that deal.
And Valdes appears happy to deputise for De Gea, telling MUTV: "Always in my career, I have played to help my team-mates, to help my coach and to help everybody. I am a part of the team."
He added: "I think now, in the moment, De Gea is the best goalkeeper in the world."
However, Valdes' arrival could lead to reserve keeper Anders Lindegaard leaving Old Trafford.
The Denmark international, 30, arrived in a £3.5m deal in January 2011 but has made only 19 Premier League appearances.
United's two other goalkeeping options are 21-year-old Sam Johnstone, who is on loan at Doncaster, and 24-year-old Ben Amos, who was criticised by Van Gaal for letting in Miralem Pjanic's 60-yard lob against Roma in pre-season.
Before last season started, Valdes confirmed he would leave Barcelona at the end of that campaign.
However, he tore an anterior cruciate ligament in March and missed the World Cup.