The referee immediately presented the NK Jelengrad footballer with a red card for "unsportsmanlike conduct".
Speaking to 24 Sata, Gazdek defended his actions, claiming the animals create "unhygienic conditions" for players.
"Chickens constantly enter the field. The terrain is full of faeces — these are unhygienic conditions," Gazdek said.
"I ran a little to the chickens to chase them off, I swung my foot and killed one by accident. F*** it. The referee ran up to me and showed me a direct red card."
Despite the fatal outburst, Gazdek was apologetic towards the chicken's owner, who lives on a farm directly next to the football pitch.
"Believe me, I did not intentionally kill this chicken. I apologised to the owner by letter and sent her a new chicken," Gazdek said.
"Nobody thought about it after the game — we ate goulash and enjoyed ourselves."
A pet owner himself, Gazdek asked for forgiveness from the wider football community, claiming he adores animals and meant no harm.
"I have a dog, two cats, and I also had a parrot, which recently sadly died," Gazdek said.
Gazdek's club decided not to enforce further punishment for the incident. In the end, NK Jelengrad defeated NK Jasenovac 8-1 during a one-sided encounter.