Tiger Woods knows as much as any athlete about the loneliness, frustration and challenges of battling back from injury.
So when Kevin Durant limped out of game five of the NBA Finals on Monday just 12 minutes into his comeback, the former world number one knew it was serious.
Durant, who has suffered an Achilles injury, had only just returned to the Golden State Warriors line-up after a month-long layoff with a calf problem.
Woods, who spent nearly two years out of golf as he battled a long-running back problem, said Durant's immediate reaction on court spoke volumes.
"It was sad," Woods said Tuesday at the US Open. "As athletes we've all been there to that spot when you just know it, that something just went, and can't move, can't do much of anything.
"And you can see it on his face, how solemn his face went. He knows it when things pop. You just know. And I've been there."
Woods, who suffered an Achilles injury in 2011, said he could empathise with Durant, who almost certainly now faces several months of rehab to regain fitness.
"I know what it feels like," Woods said. "It's an awful feeling. And no one can help you. That's the hard part.
"And whether he has a procedure or not, or whatever it is, his offseason, what that entails, that's the hardest part about it is the offseason or the rehab."
The long journey back to fitness was the hardest part of an injury, Woods added.
"That's what people don't see, is all those long hours that really do suck," he said. "And why do we do it? Because we're competitors.
"As athletes our job is to make the human body do something it was never meant to do and to do it efficiently and better than anybody who is doing it at the same time.
"Well, sometimes things go awry. And we saw it last night with Kevin."