AC Milan have confirmed that Alexandre Pato is set for at least three weeks out through a groin injury.
The Brazilian striker suffered the injury in training on Wednesday, just four days before Milan start their new campaign at home to Sampdoria.
"In the coming days new medical tests will be carried out to determine more precisely the nature of the tear to the right adductor muscle," read a club statement.
Thursday's news is the latest setback in a long line of injury problems for Pato.
The 22-year-old missed a total of 30 games last season and was ruled out for the rest of the campaign after suffering a muscle tear in Milan's UEFA Champions League semi-final clash at Barcelona in April.
Pato recovered to feature in Brazil's run to the Olympic final but must now start the Serie A season on the sidelines.