Ronaldinho is set for a month on the sidelines after picking up a muscle injury in pre-season training.
The AC Milan star pulled up in a session on Wednesday and is set to undergo further tests to understand the extent of the damage.
The 30-year-old had been in positive spirits after committing his immediate future to the club amidst speculation he could move to America to play in the MLS.
However, the former World Player of the Year is certain to miss the Emirates Cup tournament that begins on Saturday against Arsenal.
"Last night, at the end of the day's second training session at Milanello, Ronaldinho complained of pain in his flexor muscle," read a statement on the club's official website.
"This afternoon the Brazilian will undergo medical checks."