His uncertainty was magnified when he lost in the final of his first tournament to Horacio Zeballos, an Argentine ranked 73rd who had never won a title before.
"I felt a lot of pain in my knee," Nadal said. "I was more worried about other things than (whether I would) win or lose that match in that moment."
Memories of that painful defeat in Chile, along with the worrisome layoff that preceded it, made Nadal's latest French Open title Sunday that much sweeter. He became the first man to win eight titles at the same Grand Slam tournament when he beat fellow Spaniard David Ferrer in the final 6-3, 6-2, 6-3.
Since his return, he has won seven titles in nine tournaments, with losses only to Zeballos and top-ranked Novak Djokovic in Monte Carlo. He'll take a 22-match winning streak to Wimbledon in two weeks.
Following Sunday's victory, Nadal sat next to the French Open trophy and discussed his comeback. When asked about his troublesome knees, he managed a smile.
"My knee, not knees. I am lucky that is not both. It's only one," he said. "Some weeks I didn't feel well, but the last couple of weeks I start to feel my knee better. I am still going week by week, day by day."
In the past, Nadal has played a Wimbledon warm-up tournament on grass, but the 27-year-old pulled out of Halle this week to rest before heading to London. After years of grinding away on courts around the world, curtailing his practice and tournament schedules are a necessity now.
That didn't hurt him in Paris. The King of Clay broke the men's record for match wins at Roland Garros, where he improved to 59-1, with his lone defeat against Robin Soderling in the fourth round in 2009.
In the wake of his five-set semifinal victory over Djokovic, Sunday's final seemed anticlimactic. But not for Nadal, not when he was hoisting his 12th Grand Slam championship trophy and his first since that long enforced break.
"This one is very special one," he said. "When you have period of time like I had, you realize that you don't know if you will have the chance to be back here with this trophy another time."
Andre Agassi found it tough enough to win Roland Garros once — to complete his career Grand Slam in 1999. He predicted that Nadal's title total at the French Open will never be matched.
And Agassi said Nadal might not be done winning in Paris, or at the other major tournaments.
"Hopefully he's smarter with his body moving forward," Agassi said. "And I think he will be, because he has felt the price tag of making bad decisions or playing too much, or he knows how fragile it all can be. I think he's going to start to focus a lot more on being ready for these events. This is good for tennis. We need him around as long as possible."
Agassi's ranking once dropped to No. 141, and he said it took him two years to mount his comeback to win the French Open. Mindful of that experience, he finds Nadal's return from his knee injury remarkable.
"To watch him come back and do what he has done tells you a lot about his psyche, tells you a lot about how he spends time, tells you a lot about his decision-making, tells you a lot about his heart, about his work ethic," Agassi said. "To miss that kind of time and to do what he's done, I've never seen it."
Nadal held his index finger aloft after beating Ferrer. But because he was defending so many points from last year at Roland Garros and Ferrer earned more points by reaching his first Grand Slam final, Nadal will slip from fourth to fifth in this week's rankings, with Ferrer moving up a spot.
"It's strange, no?" Ferrer said. "I lost the final against Rafael, but I am going to be No.4 and him No. 5."
With a smile he added, "I prefer to win here and to stay No. 5."
Nadal may be No. 5, but he'll be among the favourites at Wimbledon.
So will Roger Federer, even though he showed further sign of decline at Roland Garros, losing in the quarterfinals to Jo-Wilfried Tsonga. Federer won his 17th and most recent Grand Slam title at Wimbledon a year ago and can't be dismissed as a threat.
Britain's Andy Murray, who won the Olympic gold medal at the All England Club last year, and top-ranked Djokovic will also be contenders at Wimbledon. The tournament hasn't had a defending men's champion repeat since 2007, which makes it much different from the French Open.
"Rafa is one of the possible winners," said his coach and uncle, Toni Nadal. "But how many are there who can win it? Djokovic, Federer, Murray. At Wimbledon it's very different in that a lot of players can win. At Wimbledon, the surface is different, the ball goes a lot faster. We will see what will happen when we arrive. We'll try and win the first match and see what happens."
AP Tennis Writer Howard Fendrich and AP Sports Columnist John Leicester contributed to this report.