The Brazil international picked up an ankle injury in training and could be forced to sit out Saturday's Serie A encounter at the Ennio Tardini
The Brazil international twisted his right ankle during Wednesday's training session and limped off the pitch to receive treatment.
It is not yet known how long the 28-year-old will be out of action for due to the knock, but Milan fear that the former Real Madrid winger will not be match fit in time for Saturday's match.
Robinho will undergo a series of tests on Thursday to determine whether he will be at Allegri's disposal for the encounter at the Stadio Ennio Tardini.
The 28-year-old has netted four goals in 22 Serie A appearances for the Rossoneri in the 2011-12 campaign.