World No. 4 Rafael Nadal has confirmed he plans to kick off his clay season next week at the Madrid Masters. Nadal, 35, sustained a stress fracture in one of his ribs at the Indian Wells Masters. The initial prognosis was that Nadal would be out for four to six weeks and those prognosis turned out to be correct. Nadal, a record 21-time Grand Slam champion, missed the beginning of the clay season as he pulled out of Monte Carlo and Barcelona. Last Monday, Nadal returned to the practice courts after being sidelined for four weeks. “Despite only just arriving with pre …