Despite making just five first team appearances and scoring one goal for Atalanta, United forked out a reported £37m for the 18-year-old Ivorian in the January transfer window.
Diallo has joined the Red Devils on a four-and-a-half-year contract, with the deal having been agreed with the Serie A side back in October.
United famously spent a meagre £12m on Ronaldo in 2003 and the Portuguese international was sold for a then world record fee of £80m to Real Madrid in the summer of 2009 after winning three Premier League titles, one FA Cup, two League Cups, the Champions League and the FIFA Club World Cup as well as the first of his five Ballon D’Ors with the club.
Ferdinand is adamant Diallo could go on to achieve something similar to the current Juventus forward.
"We've just bought a kid in from Atalanta and hopefully he does something," Ferdinand said on Rio Ferdinand Presents FIVE podcast.
"If you see his clips and speak to people at the club who are involved in buying him, potentially this kid could be a world-beater.
"That is the thought of Manchester United people that this kid is one they have unearthed.
"I don't want to put the pressure of Ronaldo on him, but no-one knew about Ronaldo when we bought him other than the people in Portugal.
"This kid seems similar in that sense and if you see his clips and the way people talk about him, the world is his oyster if he applies himself right."
