Ferguson believes Hernandez's form has suffered since he played for Mexico in last summer's Gold Cup.
"His form last season [2010-11] was fantastic," said the Scot. "He's found the second year more difficult, but a lot of that is down to not having a summer break for three years and playing every summer for his country.
"Next year he will be fine as we have agreed that he is going to get the requisite rest to perform in the Premier League."
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