Brig. Gen. Patrick S. Ryder, the Pentagon spokesman, told reporters that Celeste Wallander, the assistant secretary of defense for international security affairs, would represent the United States at a meeting on Ukraine in Brussels on Wednesday. He also said that the American ambassador to NATO, Julianne Smith, would represent Mr. Austin at a NATO defense ministers meeting in Brussels on Thursday.
Mr. Austin, General Ryder said, may attend the Wednesday meeting virtually if his health allows. Gen. Charles Q. Brown Jr., the chairman of the Joint Chiefs of Staff, is also expected to attend Wednesday’s meeting virtually, General Ryder said.
On Dec. 22, Mr. Austin underwent what is known as a prostatectomy, the removal of all or part of the prostate gland. He was released after the surgery but returned a week later with an infection. He was put in intensive care, and doctors said they drained excess abdominal fluid.
Mr. Austin was widely criticized for failing to immediately disclose his illness and absence to the White House, a breach of protocol that baffled officials across the government, including at the Pentagon.
He remained hospitalized for two weeks in January and returned to the Pentagon on Jan. 29.
Two experts who specialize in prostate cancer surgery said that most men who undergo prostatectomies do not need to return to the hospital in the weeks after that surgery.