A report from Fiveouncesofpain.com confirmed the news Monday afternoon, and Johnson subsequently issued an apology on his personal Myspace page.
"I'm sorry to everyone, my knee got jacked up training for my fight," Johnson wrote. "Not the best of times but I'll make it and come back stronger. I always do!"
Johnson last appeared at UFC Fight Night 17, defeating
A search for a replacement is currently underway.