When Ferguson abandoned his normal habit of giving players extended time off following World Cup duties to get Hernandez used to his new teammates on their summer tour of the United States, little can he have imagined the impact the Mexican would have.
A recent scoring burst of nine goals in 15 games has taken Hernandez to 16 for the season, 10 of which have come in the league.
He bagged two more for Mexico in their friendly win over Paraguay at the weekend.
It is no wonder Ferguson has likened the 22-year-old to one-time 'supersub' Ole Gunnar Solskjaer, who began his managerial career at Molde with a defeat just over a week ago.
With hugely important fixtures looming in three different competitions, the United boss knows Hernandez is going to be a key man.
"Javier has had a fantastic season," Ferguson told the US-based satellite station Sirius XM. "We are just keeping an eye on him because he played in the World Cup last year and this is his first season in the Premier League.
"We are trying to keep him as fresh as we possibly can for the important games we have coming up."
However, Ferguson accepts he could have asked nothing more of a player who was an unknown in the UK when he joined United from Chivas last spring.
"He is a marvellous player," Ferguson added. "He is a great trainer. He is a good type. His attitude is fantastic. He is a really outstanding boy."
Ferguson is in the United States to launch Manchester United's 2011 preseason tour.
A five-match tour will open in Boston on July 14 and conclude with a high-profile meeting with fellow Champions League rivals Barcelona in Washington on July 30.
United have confirmed they will face the Major League Football All-Stars team at the Red Bull Arena in New Jersey on July 27.