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.
The Hammers have "unreservedly condemned" the defender after videos emerged on social media of him kicking and slapping his pet cat.
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.
"I know how people feel, but I'm also a football manager here.
"My feeling was that Kurt has apologised and I understand a lot of people will not just be accepting of an apology. But to me he came out and [apologised] honestly and I had to do my job."
Zouma, who was booed by both sets of supporters during Tuesday's match, said in a statement earlier on Tuesday: "I want to apologise for my actions. There are no excuses for my behaviour, which I sincerely regret."
An Essex Police spokesperson said: "We have recently been made aware that this incident may have taken place in Essex and we are liaising with the RSPCA and urgent enquiries are ongoing."
'Something we didn't expect of Kurt'
Moyes reiterated his stance in his post-match news conference, saying that the impact of the distressing footage had been felt throughout the team.
"I have spoken to [Zouma] and we will move on as much as we can," said the 58-year-old.