Robben, who is currently with Bayern Munich, came close to moving to Old Trafford earlier in his career, but instead joined Chelsea in 2004.
Ferdinand, who departed Old Trafford this summer after running down his contract, has also branded the 30-year-old "the outstanding player" of the 2014 World Cup thus far.
"Arjen Robben has been the outstanding player of the tournament for me so far, and not for the first time I've being thinking 'if only' about the missed opportunity Manchester United had to sign him when he was young," he wrote in the Mail on Sunday.
"He should have been a United player. He would have fitted in. He had a brilliant breakthrough season with PSV in 2002-03, a campaign in which he turned 19, and Sir Alex Ferguson wanted to sign him.
"United made a bid of something around £5m and Sir Alex was always determined he wouldn't over-pay for any player. When that was rejected, Chelsea paid something like £12m."
Robben has also played for Real Madrid during a well-travelled club career.