After careful evaluation, Manuel Pellegrini made the decision to leave the Austrian out of the match day squad for Saturday’s trip to Bournemouth.
Arnautovic was the subject of a £36million bid from Shanghai SIPG last week, which was firmly rejected.
His brother and agent Danijel has pleaded with West Ham to let his client go to the Far East and the player’s intentions became clear when he waved goodbye to supporters after being substituted in the 1-0 win over Arsenal.
Pellegrini has now accepted that Arnautovic is now more likely to leave the Olympic Stadium than stay put.
“When you have such a high offer everyone wants to leave, but he has a contract here,” he said on Thursday.
“If I say the player must stay, the player will stay – but I think as a manager the best thing is to take the solution that is best for the player and the club, both together.
“If it’s a good deal for both parties we will arrange to be without Marko but the club doesn’t want to sell him.”
But now Pellegrini and the board are making plans to replace Arnautovic, who is now in formal negotiations with another Chinese Super League club Guangzhou Evergrande.
The club had identified three potential targets who could fill the void in preparation for his exit.
Krzysztof Piatek was being tracked by the Hammers after firing 13 Serie A goals this season for Genoa.
But the Polish international is now on the brink of joining AC Milan who held formal discussions with Genoa director Giorgio Perinetti this afternoon.
The Rossoneri have agreed personal terms with Piatek and have promised to quadruple his wages to £1.7m a year.
The clubs shook hands on a deal worth £35m plus bonuses and are set to meet again on Tuesday to formalise final details.
West Ham were also priced out of a move for Callum Wilson after Bournemouth declared their valuation of the England striker is £75million.
Maxi Gomez is now the priority for the Irons who fear they could be left without a goalscoring centre-forward for the second half of the season.
The club sent representatives to Vigo earlier in the week to try and sound out a deal for the player.
The 22-year-old set La Liga alight after arriving for just £3.6m from Defensor Sporting, scoring 17 goals in his debut season.
West Ham failed with an offer of £35million in the summer but are now stepping up their pursuit of the Uruguayan.
Express Sport understand that the board are now considering whether to stump up the extra cash and trigger his £44m release clause in anticipation of Arnautovic’s imminent departure.
West Ham have already blocked the exit of Javier Hernandez this month who had agreed terms with Valencia in fear that a lack of goals could derail their hopes of Europa League qualification.
Celta have resigned to losing their striker who has also attracted interest from Barcelona and Tottenham.
Although Gomez’s goals may prove crucial in their quest to beat the drop, extra cash to improve the squad this January could increase their chances of survival.