Players and fans of Borussia Dortmund were stunned on Tuesday night after three explosives detonated near their team bus, injuring one player.
The German team bus was en route to the Westfalenstadion for the clash, when the ugly incident occurred.
The location of the blast was roughly 13 kilometers (8 miles) from Westfalenstadion, which is now being investigated.
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Investigators found near the scene a handwritten letter that claimed responsibility for the attack.
The letter references the Berlin Christmas market attack and military operations in Syria. It is not yet clear if the letter is genuine.
The affected player, Marc Bartra underwent an operation after breaking a bone in his wrist, the team said, adding that no other players were hurt.