The 21-year-old has made 126 appearances for the Blues in all competitions.
However, the academy graduate was absent from Thomas Tuchel’s squad for the meeting with Everton at the weekend.
It was soon claimed that the youngster was open to departing the West Londoners in a bid to earn regular first-team football elsewhere.
Southampton and Leicester City are allegedly among the clubs who are keeping close tabs on the player’s situation ahead of potential approaches.
However, according to reports, the Bundesliga giants BVB are contemplating whether to make a bid of their own in the next couple of weeks.
The report adds that representatives of the winger are already in discussions with officials at the Bundesliga side.
At this moment, BVB are said to be interested in a loan agreement, rather than a big-money deal.