"The meeting with my old club was the most important match of my life," said Cassano, who will now be suspended for Samp's game against former club Roma.
"I am very upset and hope my teammates can give me a great Christmas present by winning. I don't want to cause controversy, but I was booked for nothing."
Cassano was shown the yellow card for dissent after complaining about Fiorentina's equaliser in the 2-2 draw.
"I didn't say anything! I just sat on the ground and told the linesman it was not a foul. But I thank the fans at Marassi, they gave me goosebumps. They hailed me when I was having a difficult moment and I hope to stay for a long time."
The moment he realised he would be banned for the Roma game, Cassano burst into tears, beat his fists on the ground and had to be held back by players from both teams. However, he stayed on the field and went on to score.
"If I had done what he did, I would have been sent off," pointed out Fiorentina midfielder Marco Donadel.
"Unfortunately this is football, I don't know why it is like that, but I've been carded for a lot less. The game would have changed if Sampdoria had been reduced to 10 men."