Martin Harnik says he was unhappy with the Stuttgart fans following their loss in Europe and does not apologise for his gesture.
The Bundesliga side lost 1-0 to Molde in the Europa League, but still qualified for the last 32, and during the game their supporters mocked the team for their performance which did not go down too well with the club's striker.
Harnik was seen extending his middle finger to Stuttgart fans.
"They should not party if we lose and I felt that the way they mocked us was inappropriate," Harnik said, according to German newspaper Bild.
"We gave everything in that game, so we did not deserve to be insulted like that."
Stuttgart's head coach Bruno Labbadia admitted that the gesture was a mistake but played down the incident and said that emotions were running high.
"After the game everyone was disappointed and it was very emotional. It was a mistake but in football emotions are always difficult to hold back," he said.