The Giallorossi are back in action in midweek against Coppa Italia opponents Spezia.
“After Friday's match we were all very disappointed," Fonseca said at a press conference. “Especially for our fans, who deserved a completely different performance.
“We can't change what happened, but we can start thinking that what happened should not happen again.
“The team must understand that we can only change the future by changing our attitude in the game. As I said, I'm above all disappointed for our fans."
He added, “Our ambition is to win the game tomorrow, a difficult match against a very strong opponent," he added. “Spezia are a very organised team and always have intentions of playing football.
“They are very courageous and intense in the defensive phase.
“It will be a difficult match."