Siena fans sang a song about De Rossi's father-in-law who was murdered in a gangland shooting this time last year.
“To De Rossi, I express my solidarity as a man and as a footballer for what has happened,” Giampaolo told Sky Sport 24.
He then tried to defend Siena's supporters.
“In the last three years our fans have won a disciplinary prize as the best behaved in Italia. It's an important testimony.
“My daughter has also gone into the curva on many occasions to assist in the games and has always felt at ease,” Giampaolo added.