Nadal, who will turn 38 next week, has barely played since January 2023 after being laid low by a hip injury and a muscle tear.
He had to sit out the 2022 French Open where he was the defending champion but is back in Paris for what is certain to be an emotional farewell to an event where he has lost just three times in 115 matches since 2005.
"It's good to see that he can play again, that he's not injured. I really hope that he can come back in shape because if his body leaves him alone a little bit, he has plenty to do," said Wawrinka, the 2015 champion at Roland Garros. "He is still as strong as ever."
Wawrinka added: "I trained with him on Wednesday. I love training with him, he always puts in a lot of intensity, we always have very good practice.
"If injuries leave him alone, he risks being very dangerous during the year if he manages to string together tournaments and matches."
Nadal, whose 22 Grand Slam titles are second only on the all-time men's list to the 24 of Novak Djokovic, has been handed a nightmare draw at the tournament.
The former world number one, now down at a lowly 276, faces fourth-ranked Alexander Zverev in the first round.
Nadal won the last time the two met at Roland Garros in 2022 when Zverev suffered a serious ankle injury and was forced to quit their semi-final.
Wawrinka believes that Nadal's aura of clay-court supremacy may have been dented by his recent injury troubles.
"There are things he does less well than before but it's because of injuries," said Wawrinka.
A former world number three, now at 97 in the rankings, Wawrinka was also handed a tough opener at Thursday's draw.
He faces fellow three-time Grand Slam champion Andy Murray, who is also playing the tournament for the final time.
Three of the pair's 22 career meetings have come in Paris with Murray winning in the semi-finals in 2016 while the Swiss came out on top in the last four in 2017 and the first round in 2020.
"We have played each other several times in recent years at Roland Garros, big matches and slightly less big matches since our injuries," said Wawrinka.
He had surgery on his right knee in 2007 and his left foot in March and June 2021.
Murray underwent career-saving hip surgery in 2018. A former number one, the 37-year-old Briton is at 75 heading into the French Open which starts on Sunday.
"He's someone I know very, very well. We've played each other plenty of times throughout our careers. We've had some big injuries in recent years, but it could be a very interesting match," added Wawrinka.
"I've won few matches since the start of the year, but overall my level, physically and technically, is there. In training, things are going well so I hope to be able to win matches."
