British number one Jack Draper believes it will be "very hard" for the next generation of tennis players to "achieve longevity" because of a packed calendar.
The 22-year-old returned to court for a Davis Cup tie in Manchester on Friday - a week after his US Open semi-final in New York.
Draper was beaten in straight sets by an inspired Francisco Cerundolo as Britain lost the tie against Argentina.
"There's no doubt it's a quick turnaround, I think a lot of people in my position would have not come this week," said Draper, who has played 49 singles matches this year.