Diallo, who has three years left on his current deal, arrived at Old Trafford from Serie A outfit Atalanta in 2021. He was sent out on a six-month loan spell to Scottish giants Rangers last season, where he scored three goals in 13 appearances across competitions.
Speaking on Vibe with Five, Ferdinand said that the 19-year-old should be loaned out again to gather more experience at the top level. He said:
"Unfortunately, he just isn't ready. He went to Rangers, couldn't really get into the team and affect their team, which tells you he's not near getting into the Manchester United team. Do you know what I mean?"
"Plus, again, is he the right player? He hasn't got that explosive pace that they're maybe looking for; he's more of a player with a bit more guile, who likes to come to the ball and create like that, rather than running onto things and behind and stuff like that."
The six-time Premier League winner added:
"I just think it's a bit too early for someone like him to come in and take that mantle on. Yes, I don't think he's near enough to the first-team squad. If he'd have gone to Rangers and smashed it at Rangers, then he'd have had a chance. But because he did nothing, he's going to be a little bit off it, and he's someone we will look to loan out, I'd say."
Diallo has been included in the Red Devils' 31-man squad for their pre-season tour, where he'll hope to prove his mettle to his new boss.
Manchester United announce squad for pre-season tour
Earlier this week, Manchester United announced a 31-man squad for their pre-season games in Thailand and Australia. According to a club statement, Harry Maguire, Bruno Fernandes, Raphael Varane, Luke Shaw and new signing Tyrell Malacia have travelled to Asia.
Furthermore, 13 academy graduates will participate in the tour, including Alejandro Garnacho, Zidane Iqbal and Charlie Savage. Tahith Chong, James Garner and Ethan Laird, who have returned from loan spells, will also be involved.
United are set to lock horns with rivals Liverpool in their first pre-season friendly on July 12 in Thailand. The Red Devils will then face Melbourne Victory on July 15, Crystal Palace four days later and Aston Villa on July 23.