The pair were again impressive for their Carabao Cup win at Everton.
“They are the two players who I think are irreplaceable. Fernandes is irreplaceable, they are a way off without him. He's a vital piece of the jigsaw," Neville told his Sky Sports Podcast.
“Maguire, I think, you'd know if he was missing. My gut feeling is that they would miss him enormously.
“I know some people say he's not the best defender in the league, that he's not done brilliantly since he came for £80m, but he's a big presence in the heart of the defence.
“He's good on the ball, he's composed and he's good in the air. He doesn't make a lot of mistakes, sometimes he gets caught but he's a good centre-back, a really good centre-back and a big presence in that team.
“Him and Fernandes, I'm not sure they can [rest them] at this moment in time because Ole hasn't got the luxury to lose a game, unfortunately."