ANTWERP, Belgium -- Serena Williams, the world's sixth-ranked player, has pulled out of next week's inaugural Proximus Diamond Games due to a lingering right ankle injury, the Sanex WTA Tour announced Friday.

To replace her in the field and as the second seed, older sister and world No. 2 Venus Williams has accepted a wild card into the tournament at the Sportpaleis.

Serena Williams suffered the injury on Jan. 11 in her semifinal against fellow American Meghann Shaughnessy at the adidas International at Sydney. She also missed last month's Australian Open.

"I'm very disappointed," Serena Williams said. "I was really looking forward to visiting Belgium for the first time. But unfortunately, the healing process from my injury in Sydney has taken longer than anticipated. ... It is important for me to get back to 100 percent, especially at this early point in the year."

This marks the second withdrawl of a top-10 player from this tournament due to injury. World No. 5 Kim Clijsters of Belgium pulled out of the $585,000 event last Friday with a stress fracture in his right arm.