The Keeping Up With The Kardashians star and brother Rob stepped into the ring for the Kardashian Charity Knock Out event on Tuesday evening.
She later posted a photograph of herself taken after the event on her official website, which depicted her with a bruised eye.
"My [opponent] was a good sport, but she was tough!" she wrote. "I knew I had to do it for charity, since that's what it was all about, but man, my girl could throw a punch! Look at my black eye!"
Kardashian went on to say that Rob "ended up in the hospital with a concussion" after reportedly facing a "trained fighter".
She alleged that the unnamed man was "overheard saying he just wanted to be on TV... Rob could have got seriously hurt, it was totally unfair to Rob who was just trying to do something positive for charity".
She added: "Rob is doing fine now and my black eye will be gone soon. I hope! You can try to bring the Kardashians down but we're a strong family. A concussion and a black eye can't hold us down!"