UFC 243 has reportedly lost one of its top fights after Holly Holm was forced to withdraw from her bout against Raquel Pennington.

Per ESPN's Ariel Helwani, Holm suffered an undisclosed injury and will be unable to compete on the Oct. 5 card in Australia. 

Helwani noted it's unclear if UFC will attempt to find a replacement opponent to allow Pennington to remain on the card. 

Holm would have been making her first appearance since a TKO loss against Amanda Nunes at UFC 239 on July 6. The 37-year-old has lost five of her past seven fights since beating Ronda Rousey for the women's bantamweight championship in November 2015. 

The bout with Pennington would have been a rematch of Holm's first UFC appearance in February 2015. She won that match by split decision. 

The Holm-Pennington fight was one of five scheduled for the UFC 243 main card. It will be headlined by Robert Whittaker and Israel Adesanya in a middleweight championship unification match.