Lucas Barrios could leave Borussia Dortmund in January after the defending Bundesliga champions admitted they would not stand in his way of a move.
The Paraguay international has failed to get back into the Dortmund team on a regular basis this season after picking up an injury at the Copa America last summer.
Barrios, the club's top goalscorer in each of the last two seasons, has expressed his unhappiness at the current situation.
And Dortmund general manager Hans-Joachim Watzke admits they may have to consider selling him this winter.
"Obviously Lucas is unhappy when he is not playing," Watzke told the Bild newspaper.
"I would prefer it if he were to stay, but if he does come to us and say he wants to go then we would have to talk about it."
Meanwhile, second-division Duisburg have admitted holding a long-standing interest in Dortmund striker Terrence Noyd.
Duisburg manager told Oliver Reck told Reviersport newspaper: "Terrence Boyd is on our short-list. He is a player we are interested in.
"I am able to imagine signing the player and would favour an initial loan deal. We have monitored him for some time."