Matthias Sammer will remain an external advisor to Borussia Dortmund until 2025 after extending his contract, the Bundesliga club said Monday. “I’m always very happy to be able to count on the expertise of Matthias Sammer in many areas which don’t just include the professionals,” club chief executive Hans-Joachim Watzke said. The 54-year-old Sammer, a former Dortmund player and coach, took on the role in March 2018.