WILMINGTON, Del. — The president-elect of the United States clomped across a flag-studded stage on Tuesday, intending to introduce the economic team that, he hopes, will steer the nation through turmoil.

In the process, he introduced the country to a less welcome companion: his walking boot.

After a slip while playing with one of his dogs, a shelter German shepherd named Major, over the weekend, President-elect Joseph R. Biden Jr., 78, suffered hairline fractures in his right foot, according to Mr. Biden’s office and his doctor. The black boot was a souvenir of the injury poking out over a pant leg of Mr. Biden’s signature navy blue suit.

“Good,” Mr. Biden replied to a shouted query about how his foot felt when he arrived at the Queen theater, an event space here near his home. He proceeded to show off the boot to the cameras, quickly lifting his knee to display the contraption.

Later, after his team introductions were done and he was walking offstage, Mr. Biden was peppered with more questions about the injury. He flashed a thumbs-up sign to the assembled members of the news media.

The health of a president-elect is always an issue of vital national interest, and especially so for Mr. Biden, who at his inauguration will be the oldest president in American history. Although he released health information during the campaign, he was not always forthcoming about his health protocols in the coronavirus era.

On the campaign trail, Mr. Biden often laughed off questions about his age — despite significant reservations, especially during the primary, among some voters — instructing skeptics to watch him in action as he bounded through parades and onto stages. He also discussed his Peloton workouts and weight routines.

In a statement Sunday, Mr. Biden’s doctor, Kevin O’Connor, said the president-elect sustained the fractures in his “midfoot.” Dr. O’Connor also said Mr. Biden “will likely require a walking boot for several weeks.”

Mr. Biden spent Monday out of the spotlight, meeting virtually with staff and speaking with foreign leaders. But on Tuesday, the boot was visible at times as Mr. Biden stood behind a lectern, introducing his choices for jobs involving the economy and occasionally shifting his weight.

“He appeared to move without much difficulty, though he did favor the injured foot” as he walked in for his remarks, a reporter covering him for the press pool wrote to the other members of the news media. A Biden spokesman did not respond to more detailed questions about how the injury occurred — Was Mr. Biden playing catch with his dog? Were they on a walk? — or about how Mr. Biden was feeling.

Mr. Biden, who also has another German shepherd named Champ, has long been a dog owner. Bob Markel, a friend since childhood, said that around 50 years ago Mr. Biden told him that his two dogs at the time were named Governor and Senator.

“These were sizable dogs,” Mr. Markel recalled. “They were big, just like, apparently, the ones he’s got now, that he’s going to take to the White House.”

Former Representative Bob Brady of Pennsylvania, a longtime Biden ally, said that he “didn’t meet Major, but I met Champ,” describing the pet as “gorgeous.”

“He was probably throwing something around, it could be a toy,” he said, speculating on Mr. Biden’s injury. “I spoke with his guys. He’s fine, he’s fine.”

Mr. Biden campaigned on a message of national unity, and Mr. Brady, alluding to reports about future Biden pets, suggested that the president-elect might extend a hand to fans of felines, too.

“I heard he’s going to get a cat,” he said.