McGuire said: "Wigan have come in with a bid for Marlon and it seems the most meaningful bid, the bid is now open to discussion between both clubs.
"Aston Villa and Birmingham are still interested, but it seems Wigan are closer to a deal. We are hopeful of sorting out Marlon's future in the next few days."
With the Hammers close to signing Craig Bellamy, Harewood looks set to leave London. With Fulham and Manchester City also chasing the former Nottingham Forest striker, Wigan have jumped to the queue in the race for his signature.
Birmingham have already had a bid rejected by West Ham, but Wigan are close to hitting the Hammers valuation.