The England stopper has been sidelined since May with an ankle injury but was still included in Gareth Southgate's squad.
And Neville believes that should Maguire miss the next two group games, he would be too risky to play in the knockout stages.
"If Harry Maguire can get back to a level, he will come back in. But if he comes back in, I think if it's not against Scotland, it has to be against Czech Republic," said Neville.
"You couldn't make Harry Maguire's first game back a knockout game.
"Maguire must surface in the next two matches, otherwise I fear you won't see him in the tournament, and it would be Stones and Mings to continue."