On Saturday, Milan chief executive Adriano Galliani claimed that a deal for the Spanish goalkeeper was "99 per cent done".
A picture on the Serie A club's official website on Tuesday showed Lopez arriving at Milan airport, while a tweet from the club displayed he and fellow new arrival Pablo Armero undergoing medical tests.
Lopez usurped Real legend Iker Casillas as the club's first choice goalkeeper in the league last season, playing all but two of their top-flight fixtures during 2013-14.
However, Real have signed Keylor Navas this close-season - a move that appeared to have pushed Lopez down the pecking order at the Santiago Bernabeu.
And ahead of his move to San Siro being confirmed, Lopez was grateful for the chance to sign for Italian giants Milan.
"A new stage of my career is about to begin," he said. "I thank both clubs for giving me the opportunity to be here."
