"It was not to do with the pressures of football," the Kölnische Rundschau local daily cited a police source as saying.
The referee, 41-year-old Babak Rafati, was discovered in the bathtub of his hotel room in Cologne having cut open his veins.
He left a suicide note, which revealed that he had "personal reasons" for his attempt on his own life, the daily added.
Speculation has raged in the German media as to why Rafati had tried to commit suicide.
Some have suggested it was because he was dropped from the German international referee list. Others that it was because he was frequently dubbed the Bundesliga's worst official.
His father, Djalal, said there was no hint at his son's turmoil and that he had a steady job as a banker, living in Hannover, and was in a stable relationship.
"He never spoke to me about depression or burn-out. If he had done that, I would have reacted," the father told Cologne newspaper Sonntag Express. "He was very happy (being a referee). I can't understand why Babak did this."
Rafati was released from hospital earlier Monday, only to be re-admitted at his own request.
His actions shocked the football-mad country, with the story on several front pages, and came two years after the suicide of Germany goalkeeper Robert Enke.