World number four Casper Ruud, who lost to Nadal in the Roland Garros final last year, said he would not be shocked to see the 36-year-old lift the trophy once again.
"It wouldn't surprise me because he'll probably use these weeks and these months, as he's preparing for exactly Roland Garros," Ruud told Eurosport as part of the 'Ruud Talk' series.
The only thing that's probably on his mind these days is just to be fit, be healthy and be ready for Roland Garros."
Djokovic, who turns 36 in May, has shown few signs of slowing down and drew level with Nadal on 22 Grand Slams by winning the Australian Open.
"The only tournament is Roland Garros: if Rafa is fit there, it's exactly the opposite.