Norwegian star Vibeke Skofterud will miss this year's Tour de Ski event, a cross-country season highlight, with respiratory problems, it emerged on Wednesday. Olympic champion Skofterud has been struggling with a sinus problem and coach Egil Kristiansen said: "It's really sad for Vibeke as she had started the season very well." Skofterud, 31, has made the podium six times in World Cup races so far and stands second overall behind compatriot Marit Bjoergen. Olympic silver medallist Martin Johnsrud Sundby is also out of the Tour de Ski with a cold.