Novak Djokovic worries that Father Time may prove his chief threat in his otherwise relentless march towards sporting immortality.
Just not the Father Time that thwarts other great athletes and brings careers to a crushing halt.
Feeling fresh and able to play for years to come, the world No.1 says juggling family life with the complexities of travel during a pandemic loom as his biggest concern as he hunts down the all-time grand slam titles record jointly shared by Roger Federer and Rafael Nadal.
Djokovic edged to within two of the Swiss and Spaniard's benchmark 20 slams with a comprehensive 7-5 6-2 6-2 Australian Open final victory over Daniil Medvedev on Sunday night.
But constantly being away from his wife and two young children is weighing heavily on the super Serb.
"At times it rips my heart apart," Djokovic said after etching his name on the Norman Brookes Challenge Cup for a mind-blowing ninth time at Melbourne Park.
"I will have to revise my schedule comparing to the last year or any other season before this.
"Obviously time away from family definitely is something that has an impact on me.
"I'll have to see with these rules and regulations and restrictions in place all over the world, Europe.
"Not being able to take my family on the road is something that is a big problem for me."
Racking up majors is proving less of a problem and, even at 33, Djokovic remains as healthy and hungry as ever.
"I don't feel like I'm old or tired or anything like that," he said.
"But I know that biologically and realistically things are different than they were 10 years ago for me.
"I have to be smarter with my schedule and peak at the right time. So the slams are the tournaments where I want to be able to perform my best."
Djokovic will eclipse Federer's record 310 weeks as world No.1 next month - and that's one big relief and one less concern.
"Because I'm going to focus all my attention on slams mostly," he said.
"When you are going for No.1 rankings, you kind of have to be playing the entire season and you have to be playing well.
"You have to play all the tournaments."
His coach Goran Ivanisevic sees no sign of the big three's "unbelievable" domination ending any time soon, predicting Djokovic and Nadal to not only surpass Federer's 20 majors but also challenge Serena Williams's record open-era haul of 23.
Ivanisevic even suspects Margaret Court's all-time record 24 grand slam singles crowns is now within reach.
"Calculating the amount of slams that Rafa predicting might win French or somewhere else, myself, getting closer to maybe Roger's, Rafa's record, Serena, Margaret, look, everyone has their own journey and their own way of making history," Djokovic said.
"They've made history already.
"They made a tremendous mark in our sport.
"I'm trying to build that and develop that myself in a very unique, authentic way that is suitable to me.
"Whether I think about winning more slams and breaking records, of course. Of course, I do.
"And most of my attention and my energy from this day forward, until I retire from tennis, is going to be directed in majors, trying to win more major trophies."