"Initially the difference between our valuation and theirs was too great and the matter seemed closed. But Fulham got in touch again and that led to an agreement," Groningen director Hans Nijland told his club's official website.
"Everyone at the club is happy for Erik to make this step in the autumn of his career.
"He is 31 this year and has received a lucrative offer to play for at least six months in one of the biggest leagues in Europe."