The main card of UFC 90 underwent a drastic change when Diego Sanchez was forced to pull out of his scheduled fight against Thiago Alves due to torn rib cartilage.

Sanchez will be replaced by Josh Koscheck in the evening's co-main event.

The Sanchez-Alves fight was seen as a matchup between the two top welterweight contenders. Sanchez (19-2) has two straight decisive victories since snapping a two-fight losing streak, while Alves (21-4) has captured six straight fights, including five in a row via TKO. In his last fight, he scored a decisive win over legend Matt Hughes.

Koscheck (13-2) had been rumored to be fighting on the Dec. 10 "Fight for the Troops" UFC event, and is taking the fight without the benefit of a proper training camp.

In his last bout, Koscheck earned a decision win over Chris Lytle in July.

UFC 90 is headlined by a middleweight title fight between reigning champion Anderson Silva and challenger Patrick Cote.

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