The Uruguay striker was one of four new Hull recruits brought in on deadline day, signing from Palermo for a reported £10 million fee.
However, Hull fans will have to wait to see the 24-year-old in action after manager Steve Bruce revealed that a work permit has not yet been approved.
"Hernandez is in Italy at the moment, at the British Embassy to obtain his visa to come here after playing for Uruguay earlier in the week, so I can't see him being available for Monday," confirmed Bruce.
The good news for Hull, though, is that the club's three other signings could feature.
Mohamed Diame has returned from international duty in time to potentially make his debut against the club he left at the start of the month, while on-loan pair Hatem Ben Arfa and Gaston Ramirez have been training at Hull for several days.
Michael Dawson should start in front of his new home crowd for the first time, but Andrew Robertson is struggling with a calf problem.
Bruce knows it will take a little time for his players to acclimatise following a break.
He added: "The international break is always a difficulty and is even more so now. International games used to be Saturday and Tuesday or Wednesday, but it seems there have been games every day for the past week.
"But it is what it is. We've had 15 players away in 10 different countries so it shows how far we've come – we only had six players on the training ground at the start of this week. It's all part and parcel of being a Premier League team."
Morgan Amalfitano and Alex Song are in line to make their West Ham bows after joining from Marseille and Barcelona respectively.
James Collins is available having recovered from a hamstring injury, yet Carl Jenkinson (hamstring), Matt Jarvis (thigh), Andy Carroll (ankle) and Kevin Nolan (shoulder) will be sidelined despite returning to training.
Carroll is recuperating from an ankle ligament injury and manager Sam Allardyce is cautious on setting any comeback dates for the former Liverpool and Newcastle United striker.
"I'm not going to put a timeline on it," he said.
"He has started some jogging. But to predict a time is wrong for everybody, particularly Andy.
"When you've had an operation of that type we have to be guided by the specialist that did it, Andy himself and the medical staff, so we do not rush him back too quickly."
Both sides head into the game on the back of defeats, West Ham having lost 3-1 at home against Southampton last time out and Hull going down 2-1 at Aston Villa.
A Robbie Brady penalty settled the corresponding game last season as Hull secured a 1-0 win on the way to safeguarding their top-flight status on the club's Premier League return.
