Ferdinand left United earlier this summer following 12 years at the club that included six as a teammate of the Portuguese superstar.
During their time together, they won three Premier Leagues and the 2008 Champions League, and while the former England centre-back conceded that the Portuguese is egotistical, he claimed that the Real Madrid forward deserves all the fanfare that comes his way.
Speaking to the BBC, Ferdinand said: "What everybody misses out when they look at Ronaldo is, yes he's got an ego and loves the attention but he's worked hard for it. He's a complete professional. Possibly the best professional I've ever worked with.
"So he deserves the attention and the adulation he receives because he puts so much effort into being the best player in the world. I think he has to perform the same way he has for the past five or six years. If he's in top form then you can't count against Portugal [at the World Cup].
"You saw what he did in the qualification game against Sweden, he dragged Portugal [to the World Cup]. People need to see these players, we can't wait to see the Messis, the Neymars, the Ronaldos, and hopefully you get a young star coming through, but for Ronaldo to have a fantastic tournament, means that a lot of young kids around the world will be happy."
Much rests on the shoulders of Ronaldo if Paulo Bento's side are to enjoy a good World Cup, but the Los Blancos forward has only recently returned to training following injuries to his thigh and his knee.
However, the forward provided a timely boost for his national side by returning to the starting lineup for their 5-1 hammering of the Republic of Ireland on Tuesday evening.
Ronaldo and co begin their World Cup campaign with a mouth-watering clash against Germany on Monday.