- U.S. No. 1 John Isner will miss the Australian Open due to a bruised bone in knee
- World No. 13 complained of the injury after his loss to Ryan Harrison in Sydney
- Compatriot Harrison beaten in quarterfinals by Julien Benneteau on Thursday
- World No. 35 Benneteau will now be seeded for Melbourne grand slam in Isner's absence
The United States' top male tennis player John Isner will miss the Australian Open with a knee injury.
Isner crashed out in the second round of the Sydney International warm-up event -- where he was top seed -- to fellow American Ryan Harrison and complained of a recurrence of the injury which kept him out the recent Hopman Cup tournament in Perth.
"I am extremely disappointed to announce that I have to withdraw from the Australian Open," Isner, who had been seeded 13th for the year's first grand slam, told the ATP Tour's official website on Thursday.
"I have been feeling some discomfort in my knee and have recently learned that I have a bone bruise.
"My doctors have told me that continuing to play on the knee could result in a more serious injury, so I have regrettably decided not to compete in Melbourne and use the time to fully recover."
Isner, a winner of five titles since turning pro in 2007, has never advanced beyond the fourth round of the Melbourne grand slam. He will be replaced in the draw by a lucky loser from one of the qualifying competitions.
The 27-year-old's best performance in one of tennis' four marquee tournaments came in 2010 when he reached the quarterfinals of the U.S. Open.
Harrison chalked up his first ever win over an opponent ranked inside the world's top 15 with his 6-4 6-4 success against Isner on Wednesday, but he lost his quarterfinal match 6-4 6-2 to Frenchman Julien Benneteau.
Benneteau, the 2012 Sydney runner-up, will now be seeded at the Australian Open following Isner's withdrawal.
He will play big-serving Kevin Anderson in the Sydney semifinals after the 36th-ranked South African beat Uzbekistan's Denis Istomin 6-4 6-3.
World No. 35 Benneteau holds a 2-0 winning career record over Anderson and he is confident of extending that in their last four contest.
"He's playing good," said the 31-year-old. "He's a dangerous player with a very big serve but I know I can beat him."
Australia's Bernard Tomic also reached the last four, with the 20-year-old beating veteran Finn Jarkko Nieminen 6-7 (6-8) 6-4 6-2.
He will face either Italian third seed Andreas Seppi or Spanish No. 8 Marcel Granollers.