Rafael Nadal said Friday he is saddened by Novak Djokovic's absence from the US Open as he returns to the tournament for the first time in three years.

The Spanish legend has not played in New York since defeating Daniil Medvedev in five sets to lift the 2019 title.

Nadal has added three more Grand Slam singles titles to his haul since that victory, taking his total to 22 -- the all-time men's record.

While the 36-year-old will be looking to add to that tally over the next fortnight in New York, Nadal admitted on Friday that the absence of Djokovic left him "very sad."

Djokovic confirmed on Thursday he will play no part in the tournament after refusing to get vaccinated against Covid-19 -- placing him at odds with US government travel requirements for international visitors.

"From my personal perspective, it's very sad news," Nadal said.

"It's always a shame when the best players of the world are not able to play a tournament because of injuries or because of different reasons.

"In this case, not having one of the best players of the history in the draw of Grand Slam is always an important miss, no? Tough for the fans, tough for the tournament. In my opinion, tough for the players, too, because we want to have the best field possible."

Yet despite Djokovic's absence, Nadal is adamant that the tournament will not be diminished by the non-participation of the Serbian great, who is just one behind the Spaniard in Grand Slam singles titles with 21.

"I repeat what I said plenty of times: the sport in some ways is bigger than any player," Nadal said.

"I missed a lot of important events in my tennis career because of injuries, without a doubt. Last year I was not here. Two years ago I was not here. The tournament continues. The world of tennis keep going.

"Even if is not a good news for everyone, the world continues and the tennis will continue after me, after Novak, after Roger (Federer)."

Nadal started 2022 in blistering fashion, winning both the Australian and French Opens before an abdominal muscle injury forced him to scratch from the Wimbledon semi-finals.

He returned from that injury at the Cincinnati Masters this month but exited in the second round. Nadal said Friday he had been protecting the injury during his Cincinnati comeback.

"It's a tough injury because it's dangerous, it's risky," he said. "When you have a scar, it's a place that you put lot of effort when you are serving.

"I take it very easy in the Cincinnati, too, in the practices. The match, I try my best without putting all the effort there on the serve."

Nadal, who opens his US Open campaign against Australian wild card entrant Rinky Hijikata on Tuesday, was cautiously optimistic about his preparations.

"I am doing things the best way that I can," he said. "I hope to be ready for the action, no? That's the only thing that I can say.

"Taking care with the serve, being honest. But in general terms, yes, I am practicing at high level of intensity."