The 30-year-old Brazilian suffered a muscular injury on July 31 and had been expected to return by the start of the season.

However, he has missed the Rossoneri's first two games and will not be available before October at the earliest.

"We made a wrong diagnosis," said a member of AC Milan's medical staff, Jean Pierre Meersseman.

"We made a mistake in the first evaluation. Three days after, Ronaldo's left thigh had a bruise that was particularly big.

"On August 6, another test clarified the problem. On Thursday, Ronaldo will undergo some tests. By the start of next week, we will know more about his condition but I believe he will be able to play in a month's time."

Milan have taken four points from their first two games.