The 24-year-old striker has fallen down in the pecking order at Old Trafford following the arrival of Dutch forward Robin van Persie, and will have to compete with him, Wayne Rooney, Danny Welbeck and Dimitar Berbatov for a regular starting position.
However, Sanchez is confident that Hernandez will show his mettle to manager Sir Alex Ferguson if the Scotsman continues to maintain his faith in the Mexico international.
"They must have patience with him, he's a great player," he said. "Javier has a lot of quality that he will keep showing, what he needs is continuity because when he was given that before he was effective.
"He needs to be calm and have confidence in his ability because when there is more competition the pressure can rise."
Hernandez joined United from Guadalajara in the summer of 2010.