Lopez established himself ahead of Iker Casillas as Real's first-choice keeper in La Liga over the last two seasons.
However, the UEFA Champions League winners have signed Keylor Navas this close-season - with the Costa Rica's World Cup star expected to be coach Carlo Ancelotti's number one moving forward.
And Lopez now appears to be heading for the Santiago Bernabeu exit door, with Milan supremo Galliani saying the Spaniard is on his way to San Siro.
"The deal is 99 per cent done," Galliani is quoted by Gazzetta dello Sport as saying on Saturday.
Lopez has made 42 Liga appearances for Real since joining from Sevilla in January 2013.