Ralph Macchio and Karina SmirnoffIt looks like Ralph Macchio may have to head back to grammar school and park it on the bleachers in lieu of tonight's 'Dancing with the Stars' performance. The original karate kid, 49, is suffering from a ruptured cyst that may prevent him from putting on his dancing shoes.

"Have missed days of rehearsal this week," Macchio tweeted. "Had a ruptured cyst on the back of my knee causing acute pain. Hoping to be able to perform tonight!"

But hopefully Macchio's injury won't keep him from the dance floor. He and partner, Karina Smirnoff are one of only five couples left in the race for the coveted Mirror Ball trophy. In order to compete during tonight's show, Macchio will have to fight past the 'serious pain' and muster up some extra endurance -- all of the couples will performing two different routines tonight.