Espanyol confirmed that the defensive midfielder is to travel to Italy to complete a move from La Liga to Serie A before deadline day on Monday.
The 24-year-old came through the club's youth system and, after a loan spell at Leganes followed by a brief switch to Huesca, Lopez returned to Espanyol in 2013 before going on to play 33 times in the league.MORE: Alex Morgan upset at 159-degree temps | Transfer photos
The defensive midfielder is expected to cost Napoli around 5 million euros and will slot into the berth vacated by Switzerland international Valon Behrami, who left Serie A for Hamburg during the close season.
Lopez will be presented by the club upon the passing of his medical, which he is expected to complete on Sunday.
A statement on the Espanyol website read: "Early on Saturday morning, Espanyol and Napoli agreed terms for David Lopez's transfer.
"Due to this agreement, the Sant Cugat midfielder will fly to Italy today in order to undergo his medical and complete the transfer."