The 70-year-old's latest health scare came weeks after it emerged he had kept recent hospital stays secret and had not promptly informed President Joe Biden of his cancer diagnosis, sparking widespread criticism.

On Sunday, Austin was admitted to a critical care ward due to bladder issues and officially transferred duties to his deputy.

He "underwent non-surgical procedures under general anesthesia," his doctors at the Walter Reed National Military Medical Center outside Washington said Monday in a statement.

"A prolonged hospital stay is not anticipated. We anticipate the Secretary will be able to resume his normal duties tomorrow."

The doctors added his cancer prognosis remained excellent.

- Talks on Ukraine aid -

Pentagon spokesman Pat Ryder said Austin would no longer travel to Brussels, home of NATO headquarters, this week.

Austin is a key figure in attempts by the United States to maintain Western support for Ukraine's fight against Russia's invasion, as Republican lawmakers in Washington refuse to fund new military aid to Kyiv.

He had been scheduled to attend a meeting of the Ukraine Defense Contact Group of nations coordinating the military assistance, the Pentagon added.

Austin's health troubles also come at a time when the United States faces a spiraling crisis in the Middle East due to the Israel-Hamas war.

He effectively vanished from public view for treatment for prostate cancer in December and again in January after suffering complications.

He publicly apologized after coming under heavy political fire for not revealing the hospitalizations, and multiple probes have been launched into how the US chain of command operates when senior officials become incapacitated.

Some Republicans called for Austin to be sacked, but Biden has said he remains confident in his defense secretary.

On Monday, National Security Council spokesman John Kirby was asked by reporters if Biden had any concerns over Austin's ability to continue in his job, and he replied: "Not at all."

The Pentagon on Sunday initially said that the defense chief brought along classified communications systems and would be retaining "the functions and duties of his office."

However, officials announced a few hours later that his deputy Kathleen Hicks would be taking over.

Austin has gained a reputation as an apolitical official who eschews the spotlight, which he said played into his decision to keep his cancer diagnosis secret.

At a press conference on February 1, he said he had apologized directly to Biden.

"Frankly, my first instinct was to keep it private. I don't think it's news that I'm a pretty private guy -- I never liked burdening others with my problems," he said.

The Pentagon said his "emergent bladder issue" was not related to his cancer treatment.