Madrid - Rafael Nadal is looking forward to returning to action in the first clay-court tournament of the year in Chile next week, but the Spaniard admits that his injured knee is still a source of some pain.After missing seven months with the injury and then being forced to sit out the recent Australian Open due to a stomach virus, Nadal will take part in the ATP event in Vina del Mar as a wildcard.The 26-year-old told reporters after a training session in his native Mallorca that he is excited at the prospect of returning to top-level tennis, but there are nagging doubts as to how his knee will respond."I'm looking forward to competing again and taking part in a top-level tournament," he said."I hope the knee responds well and that it tolerates the demands of professional competition."There are still days when it bothers me but it is evident that I will need time before the knee is used to top-level competition again."Nadal won the last of his 11 Grand Slam titles to date at last year's French Open but has not played a competitive match since losing to Czech outsider Lukas Rosol in the second round at Wimbledon last June.He will enter the Vina del Mar tournament at the second-round stage, with his first match scheduled for Wednesday, February 6."I'm looking forward to returning after seven months out, to training and coming up against the other players in Chile," he added.Apart from fifth-ranked Nadal, the leading player in the Vina del Mar draw will be Argentina's world No 12 Juan Monaco, who will be defending his title.