Isner Withdraws From Australian Open MELBOURNE - The top-ranked American John Isner pulled out of the Australian Open on Thursday, citing a bone bruise in his right knee. Isner, No. 14 in the ATP rankings, pulled out of his final match at the Hopman Cup six days ago citing the same injury. "I have been feeling some discomfort in my knee and have recently learned that I have a bone bruise," Isner was quoted as saying on the tournament's Twitter account. He continued, "Doctors have told me that continuing to play on the knee could result in a more serious injury." Isner's withdrawal leaves Sam Querrey (22nd) as the lone American man ranked in the top 50 in the tournament. Isner played through the injury Wednesday in Sydney, losing to his fellow American Ryan Harrison, 6-4, 6-4. It was Harrison's first victory over a top-15 opponent. After the loss, Isner spoke candidly about his need to rest his knee. "It was a lot better than it was six days ago, but it wasn't 100 percent," he said, comparing it to when he pulled out of the Hopman Cup "What I have needs time. That's all it is. It can get worse. It needs rest is what it needs. That's the only thing I've done since I felt it last week is rest. He continued: "I will need to take time off somewhere. That's a given. It's not just going to heal. I can't play all the way through and have it heal. Isner, 27, additionally blamed the severity of his injury on continuing to practice through pain in December. For now, Isner has a full schedule laid out for the next several months, already having announced his intentions to play ATP 250-level tournaments in San Jose, Delray Beach, and Houston, a 500-level event in Memphis and the Masters 1000 events in Indian Wells and Miami. Isner, who reached the third round of the Australian Open last year, is unlikely to suffer a severe slide in the rankings because of the absence.