The Millionaires boss Jurgen Klopp is looking to sign another quality centre-back at the end of the season and he appears to have set his sights on the Senegalese stopper.
Abdoulaye Ba has a contract until June 2016 at Estadio do Dragao and a release clause of €40 million, but Borussia hope they can agree a fee with the Portuguese giants.
The 23-year-old has been under contract with Porto since 2008, and he enjoyed loan spells with Sporting Covilha and Academica before he was finally handed a senior debut for the Dragons.
Ba was recalled from the loan spell from Vitoria Guimaraes just few weeks ago as Nicolas Otamendi left the club and has since started two league fixtures for the club.
Porto boss Paulo Fonseca rates the player highly, but it is believed the Dragons would not be able to resist a big money bid in the summer.