Hernandez joined United earlier this summer in a £7million deal from Mexican side Chivas.
“Javier is a lovely lad,” said Fletcher. “He has come in and settled really well. He speaks great English and gives us another option up front.
“But strikers thrive on goals. You see the confidence they get from them. Javier will be no different.
“Hopefully he can get off to a flying start and won’t look back.”