Rafael Nadal says tennis should "wait a little bit more" and only return when it is safe for competitions to resume.
The ATP and WTA Tours remain suspended until the end of July at the earliest due to the coronavirus pandemic.
Nadal took part in a call with reporters on Thursday at a time when ordinarily he would have been in the latter stages of the French Open – a slam he won for the 12th time a year ago – but the tournament was moved to September due to the outbreak of COVID-19.
Organisers provisionally rescheduled the Roland Garros grand slam to begin just a week after the final of the US Open, which is not yet guaranteed to go ahead.
The US Tennis Association is due to make a decision later this month on whether the tournament will begin on August 31.
As things stand, Nadal says he has little desire to travel to New York to defend the trophy he won in 2019.
"If you asked me if I want to travel to New York today to play a tennis tournament, I will say no - I will not," Nadal, a 19-time grand slam winner, told reporters.
"But in a couple of months, I don't know how the situation is going to improve. I am confident that if the tournament is played, it's going to be under extremely safe circumstances. If not, in my opinion, it doesn't make sense.
"My feeling is we need to be responsible, sending strong messages, and be a positive example for the society.
"We need to understand we are suffering an unprecedented situation and my feeling is we need to come back when all the players, from all the countries of the world, are able to travel under safe circumstances. I want to see my sport being 100 per cent fair and correct.
"The key, of course, is to find a medicine that helps us to be sure we can travel and compete without being scared of having the virus and bringing back the virus home. My feeling is we need to wait a little bit more."
Nadal also said he is stepping up the intensity of his training having not properly prepared with a racket for two and a half months.
The Spanish great added: "As you can imagine, I need to take things step by step.
"I just try to avoid injuries and increase the amount of work every single week. I'm not practising every single day, I'm just practising a couple of days a week.
"I don't even feel in my mind like defending champion [at Roland Garros and Flushing Meadows]. I just feel myself like coming back from zero and we start again and that's it. It is not like a normal situation that I feel myself I have to defend this, I have to defend the other thing.
"Everybody is suffering; there's a lot of people losing lives. My mind is not thinking about if I have to play the US Open or I don't have to play the US Open [or if] I have to play Roland Garros. I'm just trying to enjoy my personal life a little bit, just trying to do the right things today.
"I need a plan, but today everything is difficult to predict so I don't want to stress myself. I don't want to put any pressure on myself. When we have the clear information, I am sure that with the team we are going to be able to find a solution."