Welbeck, who had been at the club since the age of eight, was let go to accommodate new loan signing Radamel Falcao and Ferdinand admits letting him leave to a rival could be bad business.
“It is a change of direction for United letting one of their own go,” Ferdinand told the Sun.
“Traditionally, this was not their way, adding so many players in a short period of time and having such a radical overhaul. Normally, as with me when I joined in 2002, it was about adding one piece to the jigsaw.
“Some fans still romanticise about their success and the way they brought through so many home-grown players. Unfortunately, you can’t always have that fairytale.
“Radamel Falcao and Angel Di Maria are world-class players and they have added quality in Anders Herrera, Luke Shaw and Daley Blind, but I do wonder if they will live to regret not keeping Danny.”
“I cannot believe United let him go, especially to Arsenal. That seems mad to me. He’s a real threat to defenders and, if Arsenal use him right, he will be very dangerous for them.
“Danny has everything to be a top player. English football has yet to see what he can really do because he hasn’t been getting a run of games.
“I think he felt frustrated at United because, even if he did well, Robin van Persie and Wayne Rooney would be ahead of him. At Arsenal, he will be the main man and I have no doubt he will flourish.
“Imagine the pace Arsenal will have when everyone is fit. There will be Alex Oxlade-Chamberlain with three fliers in front of him in Theo Walcott, Alexis Sanchez and Danny.
“I’m telling you, they would give Usain Bolt’s Jamaican 4x100m team a run for their money.”
