The initial payment would have been increased by £8.75m in the summer.
Hammers fans were furious when they learned a deal for Dendoncker hadn't gone through, reportedly because there wasn't time for a medical.
But now it has been revealed that a paltry transfer fee also contributed to the move failing apart. It is expected that West Ham will return for Dendoncker in the summer.
The 22-year-old is highly rated in Europe and has been scouted by the likes of Manchester United.
He is a chance to make Roberto Martinez's Belgium squad for the World Cup. And if he performs well, the amount of £4.4m would seem minuscule.