The United captain was again below his best in Wednesday night's EFL Cup third round win over Northampton Town and former teammate Neville believes although he is battling to find consistency and flow, he remains one of the club's most vital contributors.
"He's still an important player, but you can see in his performance he's not playing to the top level," Neville said on Sky Sports.
"His game is not flowing and things aren't coming easy to him. Tonight was important for him to get out there and play another 90 minutes. The worry is he ended up on the right wing again.
"The continuing change of positions will affect him. He wants to be a centre forward or a centre midfielder - he doesn't want to be stuck on the right wing. That's having a massive effect on his performance."