MUNICH, Germany -- Venus Williams withdrew from next week's season-ending WTA championships because of a wrist injury and could be penalized by the tour.

She already had pulled out of this week's tournament in Austria because of her wrist.

Bart McGuire, chief executive officer of the WTA Tour, said Friday the injury will be investigated. He said Williams could lose as much as $140,000 in year-end bonus money if her injury was not legitimate.

"Especially in the view of Venus' repeated confirmations of intent of play in the Sanex Championships, this is very disappointing news for the tour," McGuire said.

He added that Williams could face other unspecified sanctions under the tour's conduct code if the injury cannot be verified.

Martina Hingis and Monica Seles already have withdrawn from the event in Munich, leaving the WTA with seven of its top 10 players in the field. Hingis has a foot injury and Seles has declined to play in Germany since she was stabbed there in 1993.

Williams' withdrawal came a day after the United States said it would not play in the Nov. 7-11 Fed Cup in Madrid, Spain, because of security concerns.

Williams, ranked fourth in the WTA, and sister Serena could have played on the U.S. team with Jennifer Capriati, Lindsay Davenport and Seles.

Despite Venus's withdrawal, Serena has reconfirmed her intent to play in the Championships and Anke Huber qualified on Thursday for the event.

The popular German, who is retiring at the end of the year, will play her final tournament in her home country.

"It is very disappointing to lose Venus but this is where the depth of our Tour truly shines," said Tour chief operating officer Josh Ripple.

"Seven of our top 10 players will be in Munich to battle for the title including newly crowned world No. 1 Jennifer Capriati, a surging number three Lindsay Davenport, and the two Belgian stars, Kim Clijsters and Justine Henin."

The championships, with $3,000,000 in prize money, feature the top 16 qualified women's singles players in the world and top eight doubles teams.

Information from Reuters was used in this report.