The club's owners decided against axing Grant despite Saturday's limp defeat at Liverpool, instead dismissing Petrovic just four months into his job. Now they want to bring in two new coaches.
Former West Ham icon Paolo Di Canio has been considered as a forwards' coach but his appointment is thought to be unlikely, while former Brentford boss Wally Downes has been lined up to work on the defence.
Fall guy: Zeljko Petrovic has been axed as West Ham's assistant manager after just four months in the job
The club's joint owners, David Sullivan and David Gold, have also decided to lower ticket prices for the clash against thirdbottom Wigan in a bid to ensure a sell-out crowd at Upton Park.
They will make 5,000 adult tickets available for just £20 each, where prices normally range between £36 and £52.
Save our season: Hammers may turn to club legend Di Canio to work with their struggling forwards and former Reading coach Downes (R) to help the defence
With the Hammers lying bottom of the Barclays Premier League with justnine points, a club statement read: 'A full house of loyal vociferoussupporters is needed to help the team as they go all-out for victory.
'Fans are being urged to snap up tickets and show their support yet again - having once more provided terrific backing at Liverpool on Saturday.'
Sullivan and Gold are reluctant to sack Grant, 55, who has a four-year contract, but they believe he needs help.
Troubled times: Former Hammer Glen Johnson put the boot into his old club scoring in Saturday's 3-0 win for Liverpool at Anfield
When he took over in June, Grant outlined his desire to appoint Petrovic, 45, a former Yugoslavia and PSV Eindhoven midfielder, who had previously worked under Martin Jol at Hamburg.
He joined West Ham two weeks before the start of the season, but failed to gain the respect of the players during his short spell at the club.
A brief statement on the club's website said: 'The club would like to wish Zeljko for his efforts during his four months at the Boleyn Ground and wish him well for the future.'
Under-fire Grant hangs on at West Ham but No 2 Petrovic faces bootLiverpool 3 West Ham 0: Grant is safe for the time being, says chairman GoldWEST HAM UNITED FC