The former Netherlands striker also detailed how he joined United in 2012 under the impression that Ferguson would be with the club for another three years - only for the legendary Scot to retire one season later.
Speaking about Ferguson's retirement to Premier League Productions, van Persie said: "That was a bit of a shock.
"Just before I signed, I literally had the pen in my hand and I said 'One more thing Sir Alex, how much longer are you planning to stay?' And he said, 'At least three more years'.
"To be fair the reason why he stopped was family reasons and family comes first. He was one of the big reasons I signed so it was a blow but then that is football.
"Players come and go, managers too. He played 26 years and built the club up but that's life."
He added: "We did struggle because we ended up being 7th. From such a high…we were thinking about winning the Champions League and moving on.
"It was a new period as well with Scholesey coming to the end, Giggsy taking a player-coach role. It was all new.
"Moyes was not to blame, anyone who came in after Ferguson good luck to you. It was not only him to blame, it was us as well. The standards were so high but they dropped."