He revealed in an interview with Gazzetta dello Sport that he would listen to offers from Serie A sides.
He said: "I do not exclude that in the future, if a good offer came to me and the club, a proposal that was not only suitable economically but also from the perspective that it was an important club, (then) I would accept."
Atletico face Real in the Madrid derby this Saturday having won just two of their last 10 matches in all competitions.
"It's strange, we have strengthened the team and we're not getting results. Perhaps we have had too many injuries, but we're still working calmly," Forlan added.