Holly Holm is out of UFC 243.

The former UFC women's bantamweight champion was forced to withdraw from her Oct. 5 fight against Raquel Pennington because of an undisclosed injury, sources told ESPN on Friday. It's unclear at this time whether Pennington will remain on the card.

"I wanted to say thank you to all of the fans who are always supporting me," she wrote Saturday alongside a video on Instagram. "I am super bummed I can't fight next weekend. I was looking forward to seeing all of you and being able to perform there again in Melbourne. I'm staying positive and will be back to 100% soon. Just a little set back but I'll be back before you know it"

The injury will prevent Holm from returning to the scene of her greatest MMA triumph: her 2015 win over Ronda Rousey, which occurred in the same venue, Marvel Stadium (then known as Etihad Stadium) in Melbourne, Australia.

Holm vs. Pennington was a rematch of a fight Holm won at UFC 184. Coincidentally, the fighters were originally scheduled to meet at UFC 181 for the first time, but Holm was forced to pull out of that fight because of an injured neck.

UFC 243 is scheduled to be headlined by Robert Whittaker vs. Israel Adesanya for the UFC middleweight title.