Middleweight king Anderson Silva is without a challenger for a proposed April 10 UFC title defense in Abu Dhabi, UFC president Dana White confirmed Thursday on Twitter.

Silva's agreed-upon challenger, 33-year-old Brazilian Vitor Belfort, was forced to withdraw after an injured shoulder required "emergency surgery," a source close to Belfort told SI.com. Details about the injury are few. Tatame.com, which first reported news of the injury, said that the veteran mixed martial artist has been unable to use his arm for "a long time" and attributed the quote to Belfort's trainer, Jayme Sandall.

The middleweight title fight was set to headline UFC 112 at Ferrari World Theme park on Yas Island, the company's first event in the Middle East since selling a 10-percent stake to Flash Entertainment, a subsidiary of the United Arab Emirates.

Finding a suitable replacement for Belfort (19-8) who could also serve as a legitimate title challenger to Silva (25-4) might prove difficult for the UFC.

Fresh off an impressive victory Saturday in Las Vegas, Chael Sonnen is purported to be next in line. However, he is currently serving a no-contact medical suspension issued by the Nevada State Athletic Commission that expires on March 9. Sonnen, who earned a unanimous decision against Nathan Marquardt, suffered a severe cut to his head during the fight that required 27 stitches -- 15 on the outside, a dozen inside.

"With the medical suspension, with the cut, it can be a bit of a tough push," said Sonnen's trainer, Robert Follis. "But depending on what Dana White and the UFC wants, you got to play that game, and do what you think is best for your career from that standpoint as well."

Follis said, if offered, he would recommend against Sonnen (24-10, 1 NC) taking the bout.

"That wouldn't be my first choice," he said. "My first choice would be to do a solid three- to four-month training camp, where we can rally around him and bring in guys, sharpen up the tools and study Anderson."

Veteran UFC star Randy Couture, who had an easy time with Mark Coleman in a light heavyweight bout at UFC 109, said Thursday afternoon that he has not been approached to replace Belfort, nor is he seeking to do so.

The long trip and short prep time make it unlikely he'll fight in April. He is rumored to meet Rich Franklin at UFC 115 in Vancouver, BC, though Couture (18-10) said he hasn't "committed to anything."

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