RIO DE JANEIRO, Sept 12 (Reuters) - AC Milan striker Ronaldo should be fit to return from his thigh injury in three weeks, the Brazil national team doctor said on Wednesday. 'I believe in three weeks Ronaldo will be ready to resume his activities as the injury has healed,' Jose Luis Runco told Globo television. Runco denied Italian media speculation the player had used growth factor therapy. 'There has been some confusion because the day Ronaldo was here, another player, Maxi from Flamengo, was here and he had some growth therapy treatment,' said Runco. 'It seems the information was confused when it got to Italy, that's all.' Runco said growth factor therapy was not banned in any case. 'Growth factor is a worldwide technique which has been in use for more than seven or eight years and at no time has it been questioned as possible doping,' he said. The Brazil striker sustained the injury at the end of July and Milan initially said he would be fit for the start of the season. But Jean Pierre Meersseman, head of Milan's medical department, told La Gazzetta dello Sport on Monday the club had miscalculated the seriousness of the 30-year-old's injury. Ronaldo travelled to Antwerp last week for a second opinion before seeing Runco in Rio on Friday.