Borussia Dortmund have fallen to a 1-0 defeat at the hands of Athletic Bilbao in Tuesday night's pre-season friendly in Saint Gallen.
The La Liga side took the lead in the 20th minute when a counter-attack led to the ball landing at the feet of Markel Susaeta, who had the space and time to calmly slot home.
Dortmund had the chance to pull level shortly before the break when they won a penalty, but Pierre-Emerick Aubameyang's spot kick was parried away by Athletic goalkeeper Gorka Iraizoz.
Thomas Tuchel's charges will contest the German Supercup against Bayern Munich in five days' time.
