The young Englishman is going through a difficult period with the German club.
He was subbed early in their game against Bayern Munich recently, which lead to some reports in German papers about Sancho being unhappy at how he was treated by the coaching staff.
Sancho has also experienced disciplinary issues regarding tardiness to team meetings.
Fjortoft, a former Premier League player, tweeted the following about Sancho: "From a very good source in Germany: Klopp and Liverpool favorite to get Dortmund-player Sancho,' tweeted the Norwegian.
"Sancho wants to leave the club already in January."