Shinji Kagawa and Nick Powell have already arrived, with huge efforts being made to land Robin van Persie and Lucas Moura, whom the Brazilian federation insists has not been released for a medical as has been reported.
"The manager will always sign players he believes will develop into exceptional players," said Neville.
"There have been these stories about Lucas and no one knows what is going to happen with Robin van Persie.
"It is always difficult to find the right players though. Manchester United already have an excellent squad who finished equal on points with the champions last year."