Pique made 23 first-team appearances in a four-year stay at United, having moved to England as a raw teenager.
Whilst Ferdinand always felt the 24-year-old had ability, it has shocked him how much his former team-mate has flourished at the Nou Camp.
"Gerard has been phenomenal," said the England star. "From sitting on the bench at United to winning the Champions League, La Liga and the World Cup. If you had told him that was going to happen he wouldn't have believed you.
"Everyone knew how good a player he was. He had so many qualities. Maybe he wasn't suited to the Premier League. But Spain suits him down to the ground."