West Ham manager David Moyes says he is a "human being and an animal lover" but "responsible for getting results" after deciding to start Kurt Zouma in Tuesday's 1-0 win over Watford.
Zouma has apologised and the club will deal with the incident "internally".
Asked whether he was upset with Zouma, Moyes replied: "Oh, 100%."
He told BBC Match of the Day: "It's something we're all disappointed with and something we can't understand.
"He'll learn from it [but] today I had to pick a football team that gave me the best chance of winning the game as manager of West Ham.