Kobel had his breakthrough campaign last season and has developed into one of the best keepers in Europe this season, helping Die Borussen top the Bundesliga table.
Having kept nine clean sheets in 22 appearances – the third-highest in the league – the Swiss shot-stopper has also garnered interest from European heavyweights.
The Blues are among the clubs monitoring his situation, but Die Borussen are expected to keep him beyond the summer, according to Sky Germany journalist Florian Plettenberg.
Plettenberg also adds that Chelsea’s interest is not concrete, and they could jump to other options in their wishlist.
Kobel is also on Manchester United’s radar and Dortmund’s Bundesliga rivals Bayern Munich.
Kepa Arrizabalaga’s dip in form has prompted Chelsea to explore the transfer market for a new keeper.
He appeared to have had his career back on track under former manager Graham Potter after dethroning Edouard Mendy as the club’s first-choice keeper.
However, the Spaniard has struggled for consistency in a season where the Blues have hit rock bottom.
Mendy, who has dropped to the fringes, has been linked with an exit when his contract runs out this summer.
The Blues have been tracking Inter Milan goalkeeper Andre Onana, who has been one of the best players in his position in the Champions League this season.
The Nerazzurri could be forced to sell the Cameroonian shot-stopper if they fail to win the Champions League or miss out on the top-four spot in Serie A.
Chelse are reportedly on the verge of appointing Mauricio Pochettino as their new manager.
