In a shocking twist to an already surprising day, UFC president Dana White has released longtime veteran Nate Marquardt after the fighter was ruled out of Sunday's UFC on Versus main event.

The company president made the announcement through social media on the new video website Tout.com.

"Not only is he out of this fight and out of the main event on Versus, he will no longer be with the UFC," White said.

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"I was looking forward to my welterweight debut. I'm sorry I let everyone down," Marquardt said in a short statement released to MMA Fighting.

Marquardt was to make his welterweight debut after 14 fights in the promotion as a middleweight. He arrived to the weigh-in venue on Saturday intent on making the 170-pound limit, but after beginning the process, Pennsylvania athletic commission officials refused to grant him clearance to fight.

Representatives from the commission were not immediately available to explain the decision.

A source in Marquardt's camp said the fighter believed he could make weight before commission members ruled him out.

Charlie Brenneman replaced Marquardt and will face Rick Story on the card.

If it is the end, it's an unceremonious finale to the UFC career of a fighter who was largely considered a consummate professional. Marquardt was 10-4 in the promotion since signing in the fall of 2005. In July 2007, he became the No. 1 middleweight contender and faced Anderson Silva for the championship, but Silva defeated him via first-round TKO.

Though he continued on in the division and was considered a contender thereafter, he decided to try a drop to welterweight after his last fight, a unanimous decision win over Dan Miller at UFC 128. Unless White changes his mind, it will be the last time Marquardt fights in the octagon.