Tiger Woods has withdrawn from next week's AT&T National because he has not yet recovered from injury. The Philadelphia event was on the former world number one's schedule, but he is still not fit enough to compete, Sky Sports reports. Woods revealed the news on social networking site Twitter today. The 35-year-old - without a tournament win for 19 months and a major for three years - wrote: "Doctor's orders: sitting out the #attnational. I'll be in Philly to support the event. Feeling stronger every day, but not 100%." The prolonged absence has left some commentators wondering whether Woods will now be fit for next month's Open Championship at Sandwich. Woods has been dogged by knee and Achilles problems since The Masters in April. The injury caused him to miss his first US Open since making his debut in 1995 as Rory McIlroy drew comparisons to the young Tiger. The injury is described as a "Grade I mild medial collateral ligament sprain to his left knee and a mild strain to his left Achilles tendon". Both injuries were sustained during an awkward shot from beneath a tree in the third round at Augusta.