The Mallorcan also had a surgical procedure on his ankle in November.
This year, the 33-year-old was unable to play his Indian Wells semi-final against Roger Federer due to a recurring knee issue and skipped Miami before returning to action for the clay swing in April.
Uncharacteristic defeats in Monte Carlo, Barcelona and Madrid left him title-less through the opening four and a half months of the year for the first time since 2004 and Moya admits there were serious concerns up until Nadal turned things around by winning Rome ahead of Roland-Garros, defeating Novak Djokovic in the final no less.
“It’s been the toughest period for sure since I’m there,” Moya said after Nadal’s victory over Dominic Thiem in the Roland-Garros final on Sunday.
“Mentally, also physically because of the injury he had in Indian Wells, but most of it was mentally very tough.”
He added: “Of course, we were concerned. He gave himself the chance to keep competing every week. Every week he was playing better than the previous week and that was our goal, to get here in the best state of mind possible.
“It was very important for him to win in Rome. He realised he was back at a good level, on the right path, and that gave him a lot of confidence.”
Moya, a champion at Roland-Garros in 1998 is also from Mallorca and has known Nadal since he was a young up-and-comer. He said he had to forget about his role as a coach during the rough period Nadal went through during the spring, and instead was there for him as a friend.
“It was really hard. He really had to push himself to the limit to get back on the court, to practice, to be motivated,” explains Moya.
“He had unbelievable attitude in those bad moments and that’s what got him here today. Hats off to what he’s done this month and a half because it’s easy to play well when all the things are working well, but what he’s been through these last couple of months is showing what kind of competitor he is and that mentally he’s a genius.”