The three-floor home in the exclusive Pedralbes area of the Catalan capital is listed with real estate firm Barcelonarent.info, which specialises in selling to wealthy Russians, daily newspaper El Mundo and other media reported.
Spanish media published several photos of the inside of the house and gardens taken from the firm's website, which was inaccessible on Friday due to Internet traffic congestion.
The agency described the property as a "luxury villa in the most prestigious zone of Barcelona" in a "quiet and exclusive" area that allows for "maximum confidentiality", El Mundo reported.
The 1,000-square-metre (10,700-square-foot) mansion has seven bedrooms, 10 bathrooms, a large living room with a fireplace, and an elevator, along with a 1,300-square-metre garden and salt water swimming pool.
Cristina and her husband, the former Olympic handball player Inaki Urdangarin, bought the home in 2004 for €5.8 million and spent around €3,000,000 upgrading the property, according to Spanish media reports.
King Juan Carlos lent Cristina €1.2 million to help her buy the house, the royal palace said Monday after Spanish media reported that the loan was mentioned in an analysis of her finances carried out by the Spanish tax office.
The analysis was requested by an investigating judge, Jose Castro, who in May ordered an investigation into Cristina's tax affairs as part of a tax and money-laundering case against her husband.
Castro is investigating accusations that Urdangarin and his former business partner Diego Torres embezzled €6 million in public funds meant for sports events.
The money was allegedly placed in the non-profit Noos Institute, which Urdangarin chaired from 2004 to 2006 and of which Cristina was a board member.
Neither she nor Urdangarin has been formally charged with any crime.
The scandal has plunged Juan Carlos's family into its worst popularity crisis in his nearly four-decade reign.
Cristina, 48, a manager in the social programmes foundation of the Catalan finance group CaixaBank, moved to Geneva last month with her four children, where she will work on the firm's joint projects with UN institutions. Her husband will remain in Barcelona.