Real Madrid and AC Milan are €1 million ($1.3 million) apart on a deal that would send three-time world player of the year Ronaldo to the Italian club.
Milan vice president Adriano Galliani met with Madrid president Ramon Calderon for more than three hours on Monday but could not agree on the price and the means of payment for 30-year-old Ronaldo's move, Galliani told reporters at Santiago Bernabeu stadium.
Real Madrid is asking for €8 million ($10.3 million) and AC Milan is offering €7 million ($9 million). Under FIFA's transfer rules, the deal for Ronaldo must be completed by Wednesday.
"We will meet again tomorrow to continue negotiating," Galliani said. "We have offered seven million euros and Real want eight and we haven't agreed on the payment conditions either.
"I'm expecting to be back in Milan on Tuesday morning with Ronaldo, who will be at AC Milan coach Carlos Ancelotti's disposal in the afternoon."
Brazil international Ronaldo, who hasn't been picked for Madrid since a January 7 defeat at Deportivo La Coruna, has said his difficulties with coach Fabio Capello have forced him to look elsewhere.
A move to Milan would take Ronaldo back to the city where he spent five years with Inter Milan.