Bonucci's agent refused to dismiss speculation on Thursday amid reports of a €40million fee for the 30-year-old – also a target for Premier League champions Chelsea and Manchester City – and the news has taken former Juve captain Del Piero by surprise.
"I didn't expect it," Del Piero told Sky Sport Italia.
"It looked like a joke, the news came like a bolt from the blue. It is a very, very amazing deal, I would not have thought about such a thing."
Since moving to Turin from Bari in 2010, Bonucci has helped Juventus to six successive Serie A titles as well as three Coppa Italia crowns and as many Supercoppa Italiana trophies.
Bonucci has also featured in two Champions League finals for the Italian giants.