
Milan striker Ronaldo continues to struggle for fitness and the Serie A side have admitted they do not know when he will be available for selection.
The Brazilian suffered a hamstring injury at the end of last season and then sustained a muscle problem during celebrations with the club's supporters at the end of July.
Ronaldo, the all-time leading scorer in World Cup history, joined Carlo Ancelotti's side from Real Madrid on an 18-month contract in January.
Milan chief officer Adriano Galliani said: "He is still feeling a little pain and until we are sure he is 100 per cent fit he won't play.
"It's a medical problem, I can't say when he will come back."
Ancelotti's side travel to Siena for a Serie A clash on 16th September before their Champions League opener against Benfica at the San Siro on 18th September.