Neville believes that the exit of the two defenders will hit the club hard.
"I think it's a big risk losing Vidic and Rio at the same time," the Manchester Evening News quotes him as saying.
"There are young centre-backs coming through, Phil Jones, Jonny Evans and Chris Smalling. And I think if we're signing a new centre-back coming from a different country who hasn't played here before, the idea of having a stalwart there would help.
"I think it's a risk. But we'll see how that pans out."