The 22-year-old prefers a move to Bundesliga side Hamburg, according to reports on Wednesday.
But Groningen manager Henk Veldmate has confirmed that Fulham has stepped up their interest in the player.
“Those two clubs Fulham and Hamburg are the only ones left who are now in conversation with us when it comes to Marcus Berg,” he told The Sun.
“We have had some meetings with both clubs. We will see what happens in the next couple of days.
“But I can say both these clubs have been concrete in their interest and we know Marcus wants to leave us for a bigger club.”