Journalist Fabrizio Romano is reporting that La Liga's champions are interested in signing the Dutchman, who is available for just €25 million (£22m/$29m). No official offer has yet been made.
A move seems some way off for Dumfries, with it not yet being clear whether a deal can be done in time for the pre-season tour of Japan and South Korea this month or even the start of the season in August.