MMAFighting.com reported the news on Monday and subsequently confirmed to Bleacher Report that MacDonald is indeed off the UFC 158 fight card.
MacDonald hurt his neck while training at his home camp in Montreal, and while the severity of the injury is unknown, he will not be able to face Condit in March.
Condit was notified over the weekend that MacDonald would be unable to fight, and it's expected that he will face a replacement opponent and remain on the UFC 158 card.
The news of MacDonald's injury cancels what was set to be the UFC 158 co-main event underneath the title fight pitting Georges St-Pierre against Nick Diaz for the UFC welterweight title.
MacDonald had been gunning for a rematch with Condit ever since losing to him in 2010 and continued to stalk the former WEC champion before and after his UFC on FOX 5 fight with BJ Penn.
MacDonald dismantled Penn for the better part of 15 minutes and then immediately made the declaration that he wanted Condit next. He got his wish when UFC officials granted the rematch and placed the fight in Montreal at UFC 158.
Unfortunately, as injuries happen in MMA, MacDonald was unable to make it through his training camp and now has to sit on the sidelines and hope he can get a crack at Condit at a later time.
Meanwhile, Condit waits for word on a new opponent as the UFC searches for a top-flight welterweight to fill the spot.
UFC 158 already features some of the division's top fighters booked on the card, but a few names exist that could jump in on short notice if willing.
Former Strikeforce champion Jake Shields called for a fight against Condit when speaking to Bleacher Report earlier this month, and actually has a win over him from a fight the two had in 2006 while competing in the Rumble on the Rock promotion in Hawaii. Shields said specifically at the time he would even be willing to step in on short notice to face Condit at UFC 158 if anything happened to MacDonald.
Two other names that could receive a call from matchmaker Joe Silva include former Strikeforce welterweight champion Tarec Saffiedine or Tyron Woodley, fresh off of his first-round destruction of Jay Hieron at UFC 156.
It's unknown at this time, however, if any of those three will get the call or if Carlos Condit will face an entirely new opponent.