The Borussia Dortmund defender says he "had a blackout" following his side's 2-0 DFB-Pokal final loss to Bayern Munich.
Eye-witnesses reported seeing the 25-year-old urinating against a pillar inside the historic Hotel Berlin before police were called after a night of partying with his BVB teammates in the wake of their cup final loss.
Grosskreutz, who was guilty of a mistake in the buildup to Arjen Robben's opener in the final, explained that he had allowed himself to indulge more than he intended due to the disappointment of the defeat and expressed remorse for his actions.
"I was totally frustrated after the game," he was quoted by Bild am Sonntag. "We had planned so much, we really wanted to win the cup. I had a blackout. I'm sorry."
This latest indiscretion came after another incident earlier in May where Grosskreutz threw a doner kebab in the face of a Koln fan during a night out with Dortmund players, and has led to a stern warning from Germany boss Joachim Low.
"[Germany team manager] Oliver Bierhoff and had a serious talk with Kevin," the 54-year-old said. "National players are role models, on the pitch as well as off it. We reminded him of this and made it clear to him that such a thing should not happen again.
"Kevin is still young — he is impulsive, he has heart and passion. He shows it when he stands on the pitch. You must also see that Kevin has always behaved properly with the national team. This incident occurred with Borussia Dortmund and there the organizers have already responded."
Grosskreutz is a part of the Germany squad for this summer's World Cup, with the Nationalelf preparing for their first Group G game with Portugal on June 16.