After being booked for dissent following protestations to the referee, Pescara midfielder Muntari left the pitch, leaving his team to play the final few minutes of their 1-0 Serie A loss to Cagliari with 10 men.
And, now the former Ghana international has received support from Del Piero.
"You handled things perfectly, you're setting the example for tomorrow. You did everything right," the Italian wrote of Muntari on his official Twitter account.
On what happened, Muntari explained after the game: "They were chanting against me from the start. In the first half, I saw that there were some children in the group and so I turned to their parents and gave them my shirt to set an example.
"The issue continued with another group of fans. I was reasoning with them, but then the referee told me I had to let it go.
"That's when I got angry. Because instead of stopping the game, he decided to punish me."