Rio Ferdinand has told The Sun that Manchester United may come to regret allowing Danny Welbeck to join Arsenal.
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Ferdinand, who ended his 12-year star at Old Trafford in the summer, believes the 23-year-old England international has yet to show his full potential and that Arsenal may offer the right environment for him to prove his worth.
"I cannot believe United let Danny go, especially to Arsenal," he said. "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."
Ferdinand, now playing for Queens Park Rangers, joined United in a big-money move from Leeds United in 2002 but he feels the transfer business conducted during Sir Alex Ferguson's reign was very different to the club's spending in recent months.
"It is a change of direction for United letting one of their own go," he said. "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 Ander Herrera, Luke Shaw and Daley Blind, but I do wonder if they will live to regret not keeping Danny."