Frei has not been guaranteed a starting berth at Signal Iduna Park since the arrival of Jurgen Klopp as manager in the summer.
The striker, who is the club's leading scorer with nine Bundesliga goals, has been linked with Tottenham, Napoli and Paris St Germain.
Frei moved to Dortmund from Stade Rennais in June 2006 and has scored 31 goals in 69 Bundesliga games, with his current contract due to expire next summer.
Certain truthHe told Kicker: "Those sort of rumours always bear a certain truth.
"I have always enjoyed a brilliant backing from the fans and the team, I signed a four-year deal when I arrived and it is also a valid deal next season.
"Until now I am here and I will also be here tomorrow."
Frei admitted that he does not enjoy the most cordial of relationships with Klopp but claimed that they do not allow their differences to affect the club.
He told Swiss tabloid Blick: "We are working together in a professional way, but we will are never likely to end up friends."