"The player is suspected of extreme unfavourable sporting behaviour in the Oct. 18 game between Cologne and Hanover 96," the DFB said in a statement.
"Andreasen is suspected of knowingly using his right arm to put the ball into the goal."
The 32-year-old Danish midfieder scored against the run of play, charging into the box at a corner and putting the ball into the net at the far post with Cologne players instantly calling for handball.
Television replays showed Andreasen clearly used his hand but referee Bastian Dankert and his assistants missed it and accepted after the game they had made a wrong call.
Andreasen also admitted it was a handball but said he did not realise it at the time because "everything happened so quickly."
"I made a motion in the direction of the ball, it all happened very quickly," he told reporters. "The ref could have blown the whistle of course. That was clearly handball."
(Reporting by Karolos Grohmann, editing by Ed Osmond)
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