"Last night, at the end of the day's second training session at Milanello, Ronaldinho complained of pain in his flexor muscle," a statement read on Milan's site.

"This afternoon the Brazilian will undergo medical checks."

Ronaldinho is set to miss the weekend's Emirates Cup in London, with reports suggesting he could be out for a month.

Milan start their Serie A season against Lecce on the 26th of August.