Striker Romelu Lukaku returns from a month-long lay-off needing to live up to manager Roberto Martinez's assessment of him being "a complete number nine" if Everton's season is not to fade in the final third.
The Belgium international, on loan from Chelsea, has missed four matches with an ankle injury but his return to fitness could not have been better timed after back-to-back league defeats have left the Toffees 11 points adrift of fourth-placed Liverpool.
Everton went into the Merseyside derby at Anfield, in which Lukaku sustained his injury, on January 28 just a point behind their near-neighbours but have dramatically fallen off the pace after losing that match - not helped by the postponement of a home game against Crystal Palace.
Lukaku, 20, has scored just once since the end of November but comfortably remains Everton's top scorer with nine league goals.
Martinez expects to see a newly refreshed and determined player when West Ham visit on Saturday.
"As a number nine he is as complete as you are going to get in world football. Something which is a rare breed - to have such a talented footballer having that target man role," said the Toffees boss.
"When you look at his age you are quite surprised by the package he brings.
"When you see him as a player you build a perception of a strong target man who is good with his back to goal and you get such a shock when you speak to him about football.
"He is a very intelligent man who wants to understand the game and I've been very impressed by how he approaches the game.
"He is good in the box as a number nine, attacks the ball well and is a good finisher, but can use the counter-attack with his pace and ball control.
"Romelu has had a terrific season and has a big role to play in our squad."
Everton run into West Ham at the wrong time after Sam Allardyce justified his board's decision to keep faith with him by guiding his side to a maximum 12 points in February to ease their relegation worries.
"West Ham deserve huge credit. I have seen it many times, when you get into a negative run it is difficult to be consistent after that," said Martinez.
"From the outside there is always the perception a team having bad results could end up with a manager losing his job but I think a manager worries about what can be done next.
"They have shown that and continuity at the club has paid incredible dividends.
"To see they have conceded only one goal in five games and had four straight wins after a good draw at Stamford Bridge shows they are a team in form."
Toffees captain Phil Jagielka has been ruled out for a fortnight with a hamstring injury so John Stones is likely to deputise in defence.
Fellow centre-back Antolin Alcaraz is fit again and comes back into the squad after spending four weeks out but on-loan striker Lacina Traore (hamstring) is unavailable.
West Ham striker Andy Carroll returns after serving a three-match suspension. Forward Marco Borriello is a doubt because of a calf problem but defender Guy Demel is expected to recover from tonsillitis.
Stewart Downing has warned West Ham that relegation from the Barclays Premier League remains a threat despite their recent surge up the table.
The Hammers have produced a four-match winning run that has lifted them out of the bottom three and into 10th place, seven points clear of danger.
Their last defeat in the Premier League was six weeks ago and on Saturday they face Everton at Goodison Park knowing a fifth successive victory would place them on the brink of survival.
The Toffees have lost three of their last four matches, but Downing refuses to underestimate them despite their recent slump.
"We're not out of the woods yet because we've still got games to win, starting at Everton," Downing told the club's official website.
"Everton is always a difficult place to go, even when they're not playing that well.
"The crowd are really on top of you, (manager) Roberto Martinez is doing a good job and his team is playing really well using a different way of playing to the past.
"We've been a bit lucky at times recently, but in the last couple of weeks it's all come together. We've been due some luck.
"Everyone is back now from injury and suspension and that's what we've been waiting for."