In a UEFA Champions League group stage match against Ajax in September 2003, he was sent off during second-half injury time after slapping Ajax striker Zlatan Ibrahimović in the face with the back of his hand. His temper has caused him further problems when in December 2005, at the final whistle of Milan's 3–2 defeat of Schalke 04 in the Champions League, Gattuso was seen seeking out and taunting Schalke's midfielder Christian Poulsen as a reaction to Poulsen's fierce marking of Kaká in the first leg. Gattuso insisted, however, that the press exaggerated the significance of the incident.