Pirlo was named Juve coach after the sacking of Maurizio Sarri on Saturday.
“Honestly, I would not have bet €1 on Pirlo becoming coach," Del Piero told Sky Italia.
“It was a surprise for me too. I was already happy with him being the choice for the 'Under 23 team, it was the right passage for him, but here, we went further, and so I wish him my good luck.
“In general, the perception of former players who become coaches is changing.
“Before there was a need for a long apprenticeship, instead in recent years we have seen Filippo and Simone Inzaghi, then Gattuso … Great champions who immediately started with great teams.
“Andrea and the comparison with Zinedine Zidane? Is it not correct to do so, Zizou had coached B team and was Ancelotti's deputy, but Pirlo has all the skills to do even greater things than Zidane.
“He knows the environment, the players and the club, I think they have spoken very clearly."