Rooney could win his 112th England cap in their first Group B game against Russia on Saturday, and Ferdinand said the 30-year-old's presence will be a vital factor for many of the younger players in Roy Hodgson's squad.
With seven of England's 23-man squad aged 22 or younger England are the youngest team in the tournament, and Ferdinand believes the importance of Rooney's experience and influence should not be underestimated.
Speaking at Hublot's Match of Friendship in Paris, Ferdinand said: "He [Rooney] is invaluable. He's somebody who all the young players now will be looking to.
"There'll be moments in that tournament, whether it's in the training ground, whether it's in the hotel or on the pitch, where they'll look around and think 'who the hell can I look at to give me a bit of guidance?' - and he's that guy.
"That's why, when people were saying he shouldn't be flying over there, you don't know what you're talking about."
The lack of major tournament experience among England's players has led to their chances of progressing to the latter stages of the tournament being downgraded by some, but Ferdinand feels fielding a lesser-known side might have its advantages.
"They're an unknown quantity," he said. "That's the thing that is on the end of my tongue all the time I speak about the team at the moment, you don't know where they are.
"They haven't got the experience in this tournament, but that's good.
"That could lead to an amount of fearlessness and then they go out and produce, which I hope."