Milan health coordinator Jean Pierre Meersseman announced the trip in an interview with the Web site Controcampo, saying Ronaldo would visit specialist Marc Martens.
The Brazil striker's knee problem ruled him out of Milan's first two games of the Serie A season - as well as the European Super Cup win over Sevilla last week.
Milan coach Carlo Ancelotti has said he expects Ronaldo back for Milan's next game against Siena on Sept. 15 - or when the squad opens defense of its Champions League title against Benfica three days later.
Ronaldo transferred to Milan from Real Madrid in January and was ineligible to play for the squad when it won the Champions League last season because he began the competition with the Spanish club.
Representatives of the Israeli Defence Ministry responded to recent reports about the possible delivery of S-300 SAM systems from Russia to Syria. Israeli Defence Minister Avigdor Lieberman said that Israel would destroy those systems
Russia is to start supplying S-300 air defence systems to Syria in the near future. The shipments will be conducted free of charge