The 25-year-old, who was on loan at Livorno from Udinese, suffered a cardiac arrest on the pitch and was rushed to a nearby hospital.
Despite the efforts of the medical staff, Morosini failed to regain conciousness.
"It's one of the saddest days of my career in football. In 26 years, I have never come across a tragedy like this," Pozzo told reporters. "I learned of Morosini's illness on television. Initially I did not fear the worst, but only an hour and a half later, we found out the news of his death from the hospital.
"It's terrible news. We had owned him since 2005, and for over six years with us, he was a good guy and a great professional.
"He made several moves on loan, but he belonged to our regular training camp. This year we had him until January, before his transfer to Livorno."
All matches in Italy this weekend have been postponed as a mark of respect to Morosini and his family.