World number one Novak Djokovic said he initially struggled to cope with the uncertainty surrounding when tennis can restart after its shutdown in early March due to the novel coronavirus.
The sport is suspended till at least mid July due to the virus, which has infected more than 3.19 million people and killed almost 227,000, according to a Reuters tally.
"For us tennis players it is important that the calendar is clear," Djokovic told Sky Sport Italia. "Officially it is the 13th of July, many people say it is difficult we will start again on that day.
"For me it is important to have a routine, I cannot keep on waiting for that day. I train every day at the gym, I run at home, I play with my kids and this is also hard work. At the beginning I was mentally a bit empty and confused, because (the timing) wasn't clear. I talked with my team, I tried to train every day, even though I didn't follow the preparation strictly."
Djokovic was in imperious form before the circuit came to a halt.
The Serb lifted the ATP Cup with Serbia, won a record-extending eighth Australian Open title in Melbourne and then completed a fifth triumph at the Dubai Tennis Championships, extending his unbeaten run to 21.
The virus has forced the cancellation of this year's Wimbledon for the first time since World War Two while the French Open was rescheduled for Sept. 20 - Oct. 4, shortly after the end of the U.S. Open.
"Officially it (the restart) is the 13th of July but the WTA in Canada (Rogers Cup) has already been cancelled, although not the men's event," Djokovic said.
"We need to see how the situation in the United States goes, because we are expected to go there in August. There's the possibility that they cancel all the events in America and that we go back to the tennis court in Autumn, maybe we can go to Rome in two-three months... let's hope we can get back to playing."
The steely-eyed Serb owns 17 Grand Slam singles titles and is just three behind Roger Federer's record haul of 20 in men's tennis.
Yet Djokovic said he considered quitting the sport in 2010 due to the pressure of expectation, after winning his first major at the 2008 Australian Open.
"Against Juergen Melzer in Roland Garros, during the quarters, this defeat was really difficult for me emotionally," he said.
"I cried a lot after this defeat because I had a moment in my life, my career, when everything happened in a fusion in which I really did not see a reason to keep on playing, I wanted to quit tennis."
Djokovic said the loss to Melzer transformed him.
"After that moment I felt I was freed," he said. "The accumulation of this pressure was making me too tired to play, I wasn't feeling the joy, I wasn't feeling free to really play in a way, a type, a style of play which was aggressive."