"If deals still have to be arranged in the evening on January 31, there is little chance that there will be a breakthrough," Dendoncker told Het Laatste Nieuws.
"West Ham seemed to me, however, a nice club to take the next step in my career."
When asked whether he was being impatient wanting a move in January rather than waiting until after the World Cup, the 22 year old said: "Many people give me that advice, but in my mind I am just ready - I long for higher. [Should] I should not let my career depend on [featuring at] a World Cup?"
The Belgium international did not rule out an eventual departure from Anderlecht.
"That's for the summer," he said, when asked on the likelihood of an exit at the end of the season.