The Philadelphia Union star is a much wanted defender, with interest from several clubs around Europe.
Leeds pushed to secure Wagner late in the summer transfer window, but were unsuccessful in their pursuit.
According to journalist Tom Bogert, the left-back will be sold either in January or next summer.
Leeds are not the only club who have a strong interest in Wagner, per the journalist, who suggests they will have a tough time securing his signature.
Wagner has 15 assists in MLS this term and is only 25.