The Maximum Fighting Championship said tests showed the American MMA fighter, who was due to face Calgary's Smealinho (The Prince) Rama, had three holes in his retina.
Two of Barnett’s doctors as well as Shelby Karpman, head physician of the Edmonton Combative Sports Commission, concluded that "Barnett would be risking serious damage to his eyes including possible blindness should he be struck again."
"I'm disappointed for Chris Barnett, but definitely more so for Smealinho Rama who trained so diligently for the title shot he desperately wanted," MFC president Mark Pavelich said in a statement Tuesday.
Rama (6-0) will be paid his basic purse and given a title fight at the MFC’s next event.
The main event will now feature bantamweights Ryan Benoit and Anthony Birchak. A middleweight fight between Allen Hope and Paul Grandbois moves from the undercard to the main card.
The 26-year-old Barnett (7-1) has not fought since April 2011 due to a contract dispute with another promotion.