Before Sunday's Ligue 1 match on the south coast, objects were hurled at the Lyon bus, leaving head coach Grosso "seriously injured" and with glass fragments lodged in his head.
According to a Lyon statement, Grosso's and assistant coach Raffaele Longo's injuries were "much more serious than expected", prompting the postponement of the game at Marseille's Stade Velodrome.
Grosso has now shared a photo showing the extent of his injury, with the former Lyon and Juventus player sporting an entirely swollen left eye and 16 stitches.
The club later said that authorities had been searching for the people who had committed the crime and that a bottle was directly to blame for Grosso's injuries.
Gianluca Di Marzioreports that French police have already detained nine people in relation to the incident, and they are still looking for further suspects. Five police officers were hurt in addition to Grosso and Longo.