The Serbian centre-half had seemed set to move to the Riverside during the summer but the deal fell through as Subotic required surgery, resulting in a lengthy spell on the sidelines.
The 28-year-old has now returned to fitness but he is yet to feature for BVB this season, although he has had two outings for Dortmund's second string.
Subotic is under contract at the Westfalenstadion until 2018 but head coach Thomas Tuchel remains keen to offload the defender.
The player's agent, Frieder Gamm, has now encouraged potential suitors to make a move in the January window and Boro may be tempted to reignite their interest.
Gamm told Starsport:
There were several options from all over Europe last summer but the rib operation had priority at that time. There was serious interest from several clubs but due to the operation a transfer did not take place
Everything is possible in football