The former Manchester United and Real Madrid forward joined the east London side from German side Bayer Leverkusen in a £16m move.
Hammers supporters will be hoping it proves a coup given the huge fees being paid for other strikers such as Romelu Lukaku and Alvaro Morata by Premier League clubs.
And they have been given further cause for optimism after video emerged of Hernandez – better known as Chicharito – scoring a great volley during training.
In the clip, the 29-year-old waits just outside the penalty box for a cross to come in.
As it comes towards him, he swivels his body and hits a first time left-footed volley that flies into the top corner.
West Ham fans were excited about him lining up for the first game of the Premier League - against former team Man Utd.
“What a terrific goal from Hernandez in training today,” wrote one.
Another added: “Can't wait to see Chicharito make his debut.”
“The fact that #westham now has Chicharito makes my days a little bit better #coyi,” commented a third.
But the Mexican was on the bench for their friendly against Altona 93 in Germany, which kicked off earlier today.
The Premier League side are currently trailing 1-0.
