Kate will not attend Invictus Games

• Catherine, Duchess of Cambridge, will not be attending the Invictus Games, palace says


• She and Prince William are expecting their second child, royal officials said this week


• Catherine is suffering from acute morning sickness


• The Invictus Games for injured service members are backed by Prince Harry

London (CNN) -- Catherine, Duchess of Cambridge, will not attend Wednesday's opening ceremony or subsequent competitions in the Invictus Games for injured veterans in London, Kensington Palace said.

Royal officials confirmed Monday that Prince William and Kate are expecting their second child.

As during her first pregnancy, she is suffering from hyperemesis gravidarum, or acute morning sickness. The condition involves nausea and vomiting more severe than the typical morning sickness many women suffer during early pregnancy.

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Catherine is being treated by doctors at Kensington Palace and didn't accompany Prince William on a planned visit Monday to Oxford.

A decision will be made closer to the time on whether she takes part in a forthcoming visit to Malta, the palace added.

'Inspirational event'

The Invictus Games, inspired in part by the U.S. Warrior Games held in Colorado, are the brainchild of William's younger brother, Prince Harry.

Some 400 competitors from 13 nations will take part in the sporting event for injured service members from the armed forces of nations that have served alongside each other, including Britain, the United States and Canada.

In a video message to international competitors on Monday, Harry said it would be an "inspirational event."

The athletes will compete in nine sports over four days in facilities built for the 2012 London Olympics.

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'Tricky few days'

William told reporters in Oxford that the couple were thrilled and that Catherine was "feeling OK."

"It's been a tricky few days," he said. "We're hoping things settle down soon and she feels better."

The couple's first child, Prince George, was born in July 2013. The second child will become fourth in line to the British throne.

Prince Charles is first in line, followed by William, Prince George and then eventually the new baby. The new child will knock future uncle Prince Harry down to fifth.

CNN's Max Foster contributed to this report.