The England defender insisted: "One thing I'm sure of is that Ronaldo going will bring the best out in our players.
"We know he scored a lot of goals in the last two seasons for us, especially against the lower teams in the league.
"He'd get a couple of goals a game against them on a regular basis.
"But we've got players we know are capable of doing that. And now the way the team shapes up, I'm sure whoever's on the pitch can do that job and fill the gap.
"Other people are going to have to take responsibility because there are goals that have gone out of our team that need to be made up. But I have every confidence in the players we have to do that."
Ferdinand also believes the absence of Ronaldo means United will become even meaner in terms of giving away goals.
The England centre-back said: "Cristiano gave us so much going forward, his talent allowed him to be left further up the field than some other players in that position.
"I would say we will be a bit more compact in midfield and harder to break down. But we have to keep that same potency up front."