Subotic was the subject of a failed last-minute bid by Roberto Mancini at the end of the January transfer window, but Chelsea may now beat Manchester City to the 21-year-old's signature.
The Bosnian-born defender broke into the Dortmund first team last season and has attracted interest from around Europe.
However, he has a long-term deal at the Westfalenstadion until 2014 and Dortmund insist Subotic is going nowhere.
“There was no chance of Neven leaving Dortmund in January," Subotic's agent Stephen Kelly said, according to Mirror Football.
“As we know, anything can happen in football and the summer is a different story, but it will take a hell of a lot of money to get Dortmund to sell Neven.”