The AC Milan striker has this week held talks with the Hammers after they agreed a £26million move for the 29-year-old, but reports in Italy suggest the Gunners have made a late bid to snatch him from under their noses.
Arsenal are set to make their move for Bacca with another of their top targets, Gonzalo Higuain, seemingly set for a move to Juventus, while moves for Jamie Vardy and Alexandre Lacazette have failed to pay dividends.
Last season, the 29-year-old scored 18 goals in 38 leagues as Milan slumped to a disappointing seventh place finish.
And Bacca has boosted hopes of a move to the Gunners by stating his desire to play in the Champions League.
“It’s my dream to play in Champions League and work toward winning it,” the former Sevilla star told Spanish paper AS.
“Unfortunately, the failure for Milan to reach the tournament is one of the themes of our discussions with the club.”
And Italian newspaper Gazzetta dello Sport claim Bacca would prefer a move to Arsenal ahead of West Ham, with the player himself admitting he had a number of transfer options to consider.
The Hammers have been pushing to make a marquee signing ahead of their first season at the Olympic Stadium and manager Slaven Bilic has identified the Colombia international as a primary target, having lodged a club-record bid.
Arsenal’s need for a new striker has become all the more pressing with Danny Welbeck out until February with injury and Olivier Giroud not due to return till August after his participation with France at Euro 2016.
Alexis Sanchez is also a fitness worry having injured his ankle at the Copa America with Chile.
Currently, only Chuba Akpom and Theo Walcott are the Gunners’ only fit forward options back in training with the club.