Kicker in Germany state that Mainz are the team that will put in a bid to sign van den Berg.
They can secure him for a fee of less than 4 million, as he wants to leave the Anfield club.
The defender has been spending the season on loan at the Bundesliga club, helping them avoid relegation.
Recently, he said: "If I go back to Liverpool, they might want me to stay. If I see that I won't get much game time, then I might choose to leave. It's really important to me that I play.
"In previous years, I didn't feel like I would be starting next to Virgil. I don't know yet what my chances will be like next summer. I think I'm doing well. I can handle playing at Liverpool. I can compete. But being a starter is different. Virgil and Konate are not easy to beat. I know it will be hard."