The England international left Old Trafford on transfer deadline day to join Arsenal in a £16 million deal. Welbeck signed a four-year contract, with the option for a fifth year, with Arsene Wenger's side.
And while Beckham believes Arsenal have struck gold with Welbeck, he is disappointment with seeing a United youth product sold.
“I think Manchester United have always brought players in but we’ve also had a great scouting system that Sir Alex Ferguson put in quite a few years ago, where we did create young talent and homegrown talent and I think that’s what we’ve done over the years,” he told the BBC.
“Obviously, seeing Danny leave, he’s been there from a very young age, eight-years-old, and his heart was in Manchester so I’m sure he’s sad to leave Manchester United but, for Arsenal, I think they’ve got a young, talented English player.
“But, obviously, to see him leave Manchester United, as a Manchester United fan, is sad but I’m not a manager.”
Beckham also praised Louis van Gaal, despite the Dutchman securing just two points from his opening three Premier League games, and believes that there will be more youngsters to roll off the Old Trafford production line in the near future.
“I’m definitely not the United manager and, I think, with Van Gaal, he’s a talented manager, he’s well respected and with Manchester United, this is a project," said Beckham.
“It’s a project that’s hopefully going to last for quite a few years and hopefully we’ve still got a lot of young players coming through but seeing Danny leave, I thought he was a very talented player and definitely one for the future, and still will be, just not in Manchester.”
United followed up the sale of Welbeck with the season-long loan signing of Radamel Falcao in the early hours of Tuesday morning.