The 30-year-old Ukraine international forward scored 11 goals in 30 appearances while on loan with Hertha, before returning to England.
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However, Voronin has not started a game since his return to Anfield, sparking talk of a possible move to Germany.
Preetz told spox.com: "We are only able to buy unattached players at this point this season and there is no unattached player able to help this club.
"I am only willing to look at the situation right now and I have faith in the manager and the team."
Hertha have also been linked with a move to bring striker Ashkan Dejagah back to the club from Wolfsburg.
Source: DSG
