The most decorated Olympian of all time is dealing with a stress fracture in his right foot after a rather grueling round of golf. Michael Phelps was seen wearing a walking boot while at a mural dedication in Barcelona, Spain. When asked about the boot, Phelps said he exacerbated a previous stress fracture during a round of golf.

“Golf really is a dangerous sport,” Phelps joked after the dedication. He said he thinks he may have injured his foot when he stepped into a hole, but added that the injury has some perks.

“The good thing is, I only have to pack one shoe.”

Phelps’ coach Bob Bowman believes the former Olympian made his stress fracture worse by walking on it throughout a golf tournament.

“He hit his foot somehow in the house and then he did that tournament when he walked about 20 miles and got a little stress fracture,” Bowman told the Associated Press.

A Closer Look at Stress Fractures
As Dr. Silverman concluded in his diagnosis of Derek Jeter’s fractured ankle, stress fractures occur because of mechanical overload to a bone that can’t compensate fast enough.

“Our bodies wear down each day as we take on weight-bearing activities. When you exercise, your body breaks down faster,” said Silverman. “If your body breaks down faster than it builds up, stress fractures occur.”

Stress fractures can also develop if a person has a foot condition that alters the way their foot displaces weight. Conditions like flatfeet, high arches, or improper gait can put increased stress on your bones. It’s uncertain if Phelps has any foot conditions that would make him more predisposed to stress fractures, but walking the 6,865-yard course last weekend definitely put added stress on his feet.

Phelps would have more than enough time address the underlying issues in his foot if he decided to come out of retirement to participate in the 2016 Olympics. He dodged a question by a reporter who asked if he was completely sure he was finished with the Olympics, saying “well, golf is definitely out.”