The East London club have already agreed a club-record £26million transfer fee for the AC Milan striker, who bagged 18 goals in 38 Serie A appearances last season.
But according to Mirror Football, the Colombian international is waiting to see whether the Irons progress to the next round of the Europa League before agreeing a move to the Olympic Stadium.
West Ham face Slovanian minnows Domzale at their new stadium this evening and are looking to overturn a 2-1 deficit from the first leg at Sports Park last week.
The news follow the latest quotes from Irons gaffer Slaven Bilic, who replied when asked whether tonight’s result was pivotal to signing top transfer targets; “One or two players, yes.”
The Premier League outfit have already signed seven players this summer but are still on the prowl for a top-class centre-forward.