Reus joined Dortmund in the summer of 2012 after the club activated a clause in his contract at former team Borussia Monchengladbach.
He enjoyed an impressive debut season with Jurgen Klopp's side and he has continued to prosper at the Westfalenstadion this term.
Reports have claimed that the likes of Arsenal, Barcelona, Manchester United and Paris St Germain are all weighing up big-money bids for the attacker.
Speculation has claimed that Premier League champions United are considering a January move for Reus after scouting the player extensively.
There has also been the suggestion that United could offer former Dortmund playmaker Shinji Kagawa as part of a deal to bring Reus to Old Trafford.
Dortmund executive Hans-Joachim Watzke has acknowledged there is a clause in Reus' contract, with reports putting the figure in the region of €35million (£29.4m).
"Marco Reus possesses a release clause option in his current contract at our club," Watzke told SPORT1media. "He could leave our club due to that.
"He is, however, the only player in our first-team squad that has such a contract clause."
Reus' contract runs until 2017 and speculation has claimed that Dortmund want to hand the 24-year-old a pay rise to remove the release clause.