Last week, United re-signed France international Pogba for a world-record £89m.
In an interview with the Daily Telegraph, Pirlo – who played with Pogba at Juve before moving to New York City in 2015 – said: “On the first training session Pogba had with Juventus the players were laughing.
“We were just in total disbelief that this player with so much obvious ability was able to leave a club the size of Manchester United for free — and I think Juventus are still laughing.”
Juventus won four successive Serie A titles during Pogba’s time at the club.
“I am not saying that Juventus will have wanted to let him go,” added the 37-year-old midfielder. “But things have worked out pretty well for them.”