Roger Federer will be out of action for up to a month after undergoing knee surgery. The 17-time grand slam champion suffered the injury the day after his Australian Open run ended in the semi-finals at the hands of Novak Djokovic. “While this is an unfortunate setback, I feel grateful that up until now I have remained mostly healthy throughout my career,” the 34-year-old Swiss said in a statement. Federer has withdrawn from the World Tennis Tournament in Rotterdam (8-21 Feb) and the Dubai Tennis Championships in Dubai (22-27 Feb).