Rumors of an injury started to come out on Friday but Brown did not officially withdraw from the fight until Saturday, according to Bleacher Report:
“Sources close to the fight confirmed the news with Bleacher Report on Saturday morning. The possibility of Brown’s withdrawal was first reported by Twitter user Front Row Brian on Friday, but our sources told us that Brown’s decision to withdraw from the fight was not actually made until Saturday morning”.
It is unknown if the UFC will try to find a replacement on such a short notice. UFC on FOX 9 is scheduled for Satruday, Dec. 14 in Sacramento, CA.