Rio reveals Robben regret
Robben came close to joining United from PSV in 2004 but ultimately opted for a switch to Chelsea, who tabled a vastly improved offer for the forward.
The Dutchman, who was just 20 when he moved to Stamford Bridge, proved a big hit in the Premier League and now boasts title-winning medals in England, Spain and Germany, as well as his home country.
With a UEFA Champions League crown and 77 international caps also under his belt, Robben - currently enjoying a productive FIFA World Cup with the Netherlands - is among the world's best players and Ferdinand wishes United had made a greater effort to bring him in all those years ago.
"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."