Stuck in Toronto traffic on a sweltering summer day, Dominic Thiem is playing Pokémon Go to pass the time. While he zaps Spearows and Pidgeys in the back of the black Lexus that is shuttling him to York University, he also stretches his legs and confides, "I don't feel so great right now."

For much of the year, until Aug. 3, Thiem owned the record for most wins on the men's tennis tour, and his appearance in the French Open's semifinal, as well as tournament wins in places such as Acapulco, Buenos Aires and Stuttgart, launched him into the top 10. But a 22-year-old isn't supposed to make creaking sounds when he stretches, much less say things like, "After Wimbledon, my whole system broke down."

The Austrian entered Wimbledon in late June on a tear, having dispatched Roger Federer and Rafael Nadal, and just about all other comers. But the wear on his wiry frame started to show in London. What should have been a walkover against unseeded Jiri Vesely turned into a slugfest in which Thiem lost three straight tiebreakers in less than three hours. He blames a virus when he says, "After the tournament, I just needed to get healthier. I needed time to get over the flu."

He hopped an Austrian Airlines flight to his family's farm in Lichtenwörth, where he spent a week sleeping until 9 a.m., lounging over hourlong breakfasts of eggs and homemade bread with his mother, Karin, and getting reacquainted with his black Labrador and a pig named Rafa. "It was kind of nice to live a normal life, even for just a couple of days," he says.

Dominic Thiem has wins against Roger Federer and Rafael Nadal this season. Joe Robbins/Getty Images

But as he kicked a soccer ball around with school chums, it was hard to escape a hard truth: By playing all those matches, Thiem has taken a risky road to the top 10.

Away from the court, he is gentle and warm, with a slightly disheveled pompadour that frames an open, earnest face. He is also unfailingly polite, down to earth enough to drive a Kia after racking up $2 million in winnings this season, and so trusting that he once dyed his hair a laughable shade of yellow on a dare, expecting others would follow. (None did.)

He got into tennis when his father, Wolfgang, left his job as a local tennis instructor to join Gunter Bresnik, an Austrian legend who was coaching Boris Becker when Thiem was born in 1993. Bresnik took the boy under his wing, bringing him to tournaments around the world and training him to be tough by hiking through the Austrian Alps.

"The No. 1 priority in all his strokes is power," Bresnik says. "And that takes a long time to get into someone who is naturally calm."

As the scruff on his face attests, Thiem is a late bloomer. "Guys like me, we have a different style that makes it hard to break in easily," he says. "When I was 18, 19, I felt like I was just a boy, body wise and mentality wise. I had to fix everything together." On his 20th birthday, he was still ranked just 166th in the world.

"Now, my body has grown up," he said at the Rogers Cup last month. But the way he says it suggests that he's still unsure about how far he can push it.

"When he was 15, I knew that when Dominic became 22 or 23, he'd start competing with the big men," Bresnik says. But his boy wonder pulled out of the German Open in Hamburg on July 11. And his comeback at the Generali Open, a tournament played in the resort town of Kitzbühel, four hours by car from his home, faltered on July 20. Celebrated as a favorite and mobbed wherever he went, Thiem was upset in the first round 6-3, 7-5 by Jurgen Melzer, the 36-year-old elder statesman of Austrian tennis who hadn't won against a top-10 player in five years.

"I didn't practice or play for 10 days," Thiem says. "Then I practiced too much too early and came back to a bad situation."

As his taxi finally reaches the Rogers Cup tennis center on July 25, Thiem makes his way to a side court. Instead of retiring from Kitzbühel, he hung around for a week and earned a spot in the doubles final, which he lost with an old friend, Dennis Novak.

He says he didn't want to let down the fans who'd paid to see him. But his decision to spend a week playing doubles on clay while the hard-court season was in full swing also served as his answer to those who've criticized him for skipping the Olympics. ("I have no desire to go there," he says. "I just don't feel the Olympic spirit.")

He flew to Toronto that night, getting in at 5 p.m. and immediately going to practice. Now, the next morning, his hitting partner is Alexander Zverev, a 19-year-old German phenom who, with his flowing blonde hair, could easily be mistaken for a member of a boy band. Even though Zverev is 0-3 against Thiem, the two share an easy chemistry, and when they start to hit, the balls rise lazily over the net and then drop deep with thuds.

As the 90-minute session wears on, though, the pace gets more intense. Thiem starts drawing the racket so far back on his forehand that he seems to risk tearing his arm out of its socket. When he swings it across his body, he needs his left hand to stop it, otherwise it would seem to be ready to fly out of his hands. On the backhand, he adds another 10 pounds of heft to the ball with a wrist-whipping release. (Thiem doesn't own the shot. It's comes courtesy of Stan Wawrinka. But Thiem is the best young practitioner.)

Dominic Thiem owns seven career ATP titles, including four this season. Clive Brunskill/Getty Images

Along the way, Zverev grows more respectful, stepping farther behind the baseline and netting balls he was making earlier. Thiem, seemingly in command of all his weapons, walks off the court in high spirits. But two days later comes another crash, this one the worst yet. Down 4-1 in the first set against the big-serving South African Kevin Anderson, Thiem calls for a trainer and retires with a hip injury.

"My coach didn't expect that I'd do that well," Thiem says candidly later. "Myself, for sure I didn't expect to do that well. But we will stick to the plan." Smiling wanly, he adds, "Maybe I [should have taken] it easier, so now I have couple of problems."

Thiem has a freakish ability to recall the draws of Grand Slams going back decades. He remembers when Rafa broke out at 17, and knows that it's unlikely anyone will dominate at that age again. In tennis, 22 is the new 17, and Thiem might not hit his stride until the new 20.

In the meantime, he seems to be going through a moment of self-discovery. It's both thrilling and exhausting to watch him test how much power he can take out of his body before it starts to fight back. You feel your own bones ache when he sighs and says, "I really need some time on a beach."