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According to his twitter account, Japanese wrester Riki Fukuda sustained an injury to his left knee and will be forced to withdraw from his UFC 133 middleweight bout with Rafael "Sapo" Natal.
Fukuda made his UFC debut against Nick Ring at UFC 127. He dropped a decision to Ring in a fight that many felt he won. That loss snapped a 7 fight win streak for Fukuda.
UFC 133 will be headlined by Rashad Evans vs. Phil Davis in a light heavyweight title eliminator bout and marks the promotion's return to Philadelphia's Wells Fargo Center.
Presumably Fukuda means the accident happened on June 16th.
Update by Tim Burke - BE's # 6 middleweight prospect Constantinos Philippou (7-2, 0-1 UFC) has stepped in as a replacement and will face Natal at UFC 133 according to Natal's twitter.