The bout between Diaz and Riggs was to crown the organization’s first ever welterweight champion. The two had met before at UFC 57, where Riggs scored a unanimous decision victory over Diaz. Since that loss, Diaz has gone on to win 9 of his last 11 contests while Riggs has gone 6-4.

According to the report on GracieFighter.com, Riggs pulled out of the fight "after suffering a bad reaction to an as of yet undisclosed drug". The report noted that Riggs will be staying in the hospital for the next several weeks, and it's unknown if the problem is physical or mental.

"I heard something like, but we're still looking into it," Strikeforce executive Mike Afromowitz told MMAJunkie.com.

Riggs had last fought on June 6, 2009, defeating the controversial Phil Baroni at Strikeforce: Lawler vs. Shields via unanimous decision.

No replacement has been named for Diaz, although it is expected that Strikeforce will be announcing a new opponent for Diaz in the next couple of days. Strikeforce has also yet to name a replacement for Werdum for the event. The two other title fights, with Gina Carano (7-0) facing Cris "Cyborg" Santos (7-1) for Strikeforce's first-ever 145-pound women's title and Josh Thomson (16-2) squaring off against Gilbert Melendez (15-2) for the Strikeforce lightweight title, are still in tact.

Stay tuned to FightLine.com for further updates on Strikeforce: Carano vs. Cyborg.