The Dutch club will receive a further £370,000 if the struggling Cottagers retain their Premier League status this season.
The former Manchester United striker will now undergo a medical and discuss personal terms with the London club.
Groningen director Hans Nijland told the 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."
Nijland revealed the deal appeared to be off before Fulham made contact again over the weekend.
"Initially the difference between our valuation and theirs was too great and the matter seemed closed," he added.
"But last weekend Fulham got in touch again and that led to an agreement."