The Costa Rica international had been linked with a move to Real Betis this week, but it appears that PSV have stolen a march on the La Liga side in the race to sign the forward.
The 28-year-old is no longer considered a regular in the Fulham line-up and has not featured for the west London club since the club's 6-0 defeat to Hull on December 28.
Ruiz moved to Fulham from Dutch Eredivise side FC Twente on transfer deadline day in the summer of 2011 for an undisclosed fee.
He began his career in his homeland of Costa Rica before moving to Gent in 2006. After three years with the Belgian side he moved to Twente where he scored 35 goals in 65 appearances.
He worked under former England manager Steve McClaren during his time in Holland and helped FC Twente win the championship for the first time in their history in 2010.
Ruiz has scored once in 12 Premier League matches for Fulham this season.