By his standards, Rafael Nadal's season was a disappointment. He failed to reach a Grand Slam final and experienced long periods of self-doubt, even losing trust in his lethal forehand.

But was this just an aberration? Will the Nadal who won 14 Grand Slam titles return in 2016?

Recently, his uncle and longtime coach, Toni Nadal, spoke with ESPN.com.

What has changed for Rafa? What can he do to raise his level?

"First of all, and this is the most important thing, is the tranquility. Rafael is much more comfortable on the court now. And in this moment, he thinks about what he needs to do, and then when he gets on the court that is what he does. For many months this year, he was thinking about what he wanted to do, about this or that, but then when he came on the court, he couldn't do it. Now he can do it, and that's good. It gives him the possibility to play well."

How frustrating has this season been for you and Nadal?

For the first time since 2004, Rafael Nadal failed to win a Grand Slam title. Aurelien Meunier/Getty Images

"For me, it hasn't been difficult because I know that in life things don't always go as I want, and how Rafael wants. I know that it's not the case that just because you want to do something, that it's going to happen. In life, things don't always go the way you want, or in the direction you want, and tennis is the same, it's not special. So it's OK, because we can accept that sometimes we have good seasons and sometimes we have bad seasons. We have good tournaments and we have bad tournaments."

With victories against Stan Wawrinka and Andy Murray in the season-ending ATP World Tour Finals, are you happy with the direction Nadal is going?

"Maybe. But he also wasn't so far away from beating Roger Federer in an indoor court in Basel [recently] when Roger was playing very well. And he has beaten some good players recently. For us, the victory over Andy Murray in London was very important because Murray is the No. 2 in the world and a very good player. I think Rafael during the last two months has played so much better than earlier in the season."

Will Rafael go back to winning Grand Slams in 2016?

"Yes. I couldn't do this work if I thought that he couldn't win more Grand Slams. No, no, no, I think that he can win more Grand Slams. He can win the Australian Open in January. And he can win Wimbledon, too. The last few years, Rafael arrives at Wimbledon and he loses early, and very fast. And, in Roland Garros, for sure, Rafael can win. In tennis, you need confidence to do things. It's impossible to do anything without confidence. You can't win any good tournaments if you think you cannot and you don't believe."

Do you think that Rafa can equal and then surpass Federer's 17 Grand Slam titles?

"I don't know. I will wait until 2016 starts before I think about that, but I know that Rafael can improve and that he can play well and play to a high level."

Who had the better season, Novak Djokovic or Serena Williams?

"I think Djokovic, but Serena had a great year, too, as she also won three Grand Slams. Maybe Djokovic as he made the final of the other one [Roland Garros] and Serena lost in the semifinal of the one she didn't win [the US Open]. Sometimes this season it was impossible for anyone to beat Djokovic. With Serena, it was a little less impossible for her opponents."

What does Rafa have to do to challenge Djokovic in 2016?

"What he tries to do every day on court, which is to play more aggressively from the baseline, and to go into the net when he can, and to improve his serve."