United secured Fernandes with days remaining in the January transfer window.
He arrived from Sporting CP and has impressed in his two Premier League outings since.
Fernandes helped United defeat Chelsea 2-0 away from home on Monday night.
Neville told Sky Sports: "The problem they've got is when they come up against a team who are solid. They have problems in creativity and breaking down a team that basically sits behind the ball in numbers. That's happened time and time again. It's a well-known pattern.
"When Manchester United don't have the ball against the top teams and the top teams have to come out at them, they look like quite an exciting team, and they've had some wonderful victories this season. They've even proved difficult for Liverpool at Old Trafford.
"Ultimately, United have a pattern about them in terms of the type of games they enjoy and the type of games they don't.
"Maybe Bruno Fernandes will be the difference in certain games now at Old Trafford. They will be hoping they can get a little bit more out him in terms of creativity and assists, but there's still a lot to do for them to convince us all that they can go on a consistent run."