The Portugal international grabbed a brace in Tuesday's 3-0 win over Brighton, continuing his incredible run since joining the club in January.
But Neville thinks Ole Gunnar Solskjaer's needs to add more players of Fernandes' quality.
"This team is a lot more likeable than the one which was here two years ago when you thought Manchester United's recruitment had lost direction," he told Sky Sports.
"But I would urge some caution. Manchester United are sixth in the Premier League, they have a squad which is improving with young players.
"But there is still some work to be done in the transfer market to get this team to a title-winning team – which has to be Manchester United's ambition.
"There is more needed and a lot more needed: three or four players of high quality of the Bruno Fernandes type to get them to the point where they can challenge."