Gattuso had been experiencing vision problems in early September 2011, a few days before the season kicked off. On 9 September 2011, Gattuso crashed into teammate Alessandro Nesta whilst playing against Lazio in Milan's opening Serie A game of the 2011–12 season. He was substituted off directly afterward in the 20th minute and diagnosed with a left sixth cranial nerve palsy, resulting in double vision, an injury that could have ended his football career. He later revealed that he had seen teammate Zlatan Ibrahimović in four different positions during the opening stages of the match, and was unable to see Nesta, resulting in the pair's clash.