U.S. captain Mary Joe Fernandez announced King's addition to the team Tuesday, along with the rest of her squad, which includes surprise 2009 U.S. Open quarterfinalist Melanie Oudin, Bethanie Mattek-Sands and leading doubles player Liezel Huber.
"I have my same core group returning," Fernandez said in a call with reporters from the Australian Open.
Fernandez had been figuring that seven-time Grand Slam singles champion Williams would be a part of the team for the first time since 2007. But Williams told Fernandez she couldn't participate after injuring her hip at the Australian Open last week.
Williams stopped playing only minutes into her third-round match at the Australian Open. She was hurt during a second-round victory and then tried to play again two days later but conceded the match after seven points -- the first time in her career the 30-year-old Williams has retired from a Grand Slam match due to injury.
"Venus was going to play and, unfortunately, she got hurt during the Australian Open," Fernandez said. "I just confirmed with her a couple of days ago about her injury and that she wouldn't be able to go" to Belgium.
Her absence means neither Williams sister will play in the best-of-five series Feb. 5-6 on an indoor hard court at the 14,000-seat Antwerp Sports Palace. Williams' younger sister, 13-time major champion Serena, has not played a tournament match since July because of a foot injury.
King is 4-6 in Fed Cup play, 3-2 in doubles. She won two Grand Slam doubles titles with Yaroslava Shvedova of Kazakhstan in 2010, at Wimbledon and the U.S. Open.
While King is only 88th in the WTA singles rankings, she is No. 4 in doubles, one spot behind Huber.
"The good news about having Vania is she can play many different roles," Fernandez said. "She's very versatile. She can play both singles and doubles."
"It's pretty clear they're two of the best players to play the game. ... [But] to me, Fed Cup is very different than a regular tour tournament. ... You really approach it as one unique match and you try to do all you can to disrupt all the great things that both those players do. It's not easy, but it's been done before," said Fernandez, who led the United States to the Fed Cup final in each of her first two seasons as captain.
"We have our work cut out for us in Belgium," Fernandez said.