Hernandez is now set to return to Manchester with his new side and admits it will be an emotional time - and that he has a decision to make over whether to celebrate if he hits a debut goal for West Ham.
Last season, the Hornets' home game against the Red Devils was the only of the four to be broadcast - and saw them register a historic 3-1 win over Jose Mourinho's side.
The club, who had come within a whisker of qualifying for the Champions League in 2015/16, lost their way last term with off-the-field distractions and a crippling injury list forcing them to look down, rather than up, the table.
"I don't know - in this type of game and with these type of opportunities I will not think about celebration".
Tata Steel agrees deal to restructure British pension fund
Tata has agreed a final payment of £550m, and will also give the pension scheme a 33% stake in its United Kingdom business. The British Steel Pension Scheme said it would write to its members in the next few weeks about the new scheme.
Star Bet: West Ham's long running striker-saga reached episode 33 with the summer signing of Javier Hernandez from Bayer Leverkusen. It's an important moment for me.
"Even if I am described as the best striker in the world, or the worse striker in the world, that is something that I need to prove on the pitch", he said. It is my old club, with my old fans in my old stadium so probably I can not celebrate.
News of the midfielder's decision to remain at the club will undoubtedly delight manager Slaven Bilic, who has already seen influential duo Michail Antonio and Pedro Obiang extend their contracts with the Hammers, earlier this year. "Then of course, every players wants to use their situation in the best possible way but I know for sure that he is happy here".
'I remember him from Man City, I remember him from England and I remember him from Torino. If he plays as fast as he talks then it is going to be very exciting for West Ham.