UFC president Dana White confirmed the news to ESPN.com via text on Monday, following an initial report by USA Today. UFC 158 takes place March 16 at the Bell Centre in Montreal.
"While I was disappointed to hear that Rory MacDonald is injured, I am glad that the UFC was able to find a strong replacement for the fight in Johny Hendricks," Condit said in a statement. "He is one of the toughest welterweights in the world, and has quickly risen up the ladder in our division. We are similar in that we like to stay active and aggressive in our fights, so this should be a great fight for the fans to watch."
News of MacDonald's injury broke earlier on Monday. The Canadian welterweight had lobbied for and received a rematch against Condit (28-6) after defeating BJ Penn in December. Condit handed MacDonald (14-1) his only professional loss in June 2010.
Hendricks (14-1) was also scheduled to fight on the March 16 card against fellow contender Jake Ellenberger. A former All-American collegiate wrestler at Oklahoma State University, Hendricks has won five consecutive bouts in the UFC, three by way of knockout.
The winner of the newly announced fight will be in terrific position within the UFC welterweight division. ESPN.com currently ranks Hendricks and Condit the Nos. 2 and 3 welterweights in the world, respectively.
Condit competed for the UFC title against champion Georges St-Pierre at UFC 154 in November. He had St-Pierre in trouble after landing a head kick in the third round, but the champ went on to a unanimous decision victory.
With Hendricks no longer available to him, Ellenberger will face former Strikeforce welterweight champion Nate Marquardt on the UFC 158 card. White confirmed this bout with ESPN.com on Tuesday.
Ellenberger (28-6) expressed disappointment upon learning that he was no longer fighting Hendricks. A win over Hendricks would have placed Ellenberger, who is currently ranked seventh among welterweights by ESPN.com, near the top of most 170-pound contender lists.
"I knew you'd find a way you [Hendricks]," Ellenberger said Monday night on Twitter.
Marquardt, however, immediately took to Twitter to offer his services when word of Hendricks' removal was made public.
"Just heard [Ellenberger] doesn't have anyone to fight March  as of today," Marquardt said Monday night. "Just so happens I'm free that night."
Marquardt (32-11-2) claimed the vacant Strikeforce welterweight title on June 14, 2012, when he knocked out highly touted Tyron Woodley in the fourth round. But he would relinquish the belt in his first title defense on Jan. 12 -- dropping a unanimous decision to Tarec Saffiedine -- in Strikeforce's final event.
The fight with Ellenberger will be Marquardt's first in UFC since his release from the promotion in June 2011. The release came shortly after Marquardt failed a prefight drug test due to elevated testosterone levels.
St-Pierre (23-2) is scheduled to make his eighth consecutive title defense against Nick Diaz (26-8) in the UFC 158 main event.
ESPN.com's Franklin McNeil contributed to this report.