World No 9 Jack Draper said the ATP Tour must review its packed calendar if young players are to have long careers, after Holger Rune sustained a serious injury and joined a growing list of players breaking down as the season nears its end.

Rune said on Sunday he faced "a while" out of action with an Achilles injury that will require surgery.

The No 11-ranked player limped off the court in visible distress in the semifinals of the Nordic Open in Stockholm on Saturday and had to retire injured from the match against Ugo Humbert. He was leading 6-4, 2-2.

"It's gonna be a while before I can step on court again. It's tough. I had so much joy on court in Stockholm, and it's unbearable to think that I will not feel this energy for some time now," he posted on Instagram.

The 22-year-old Dane said his Achilles was "full broken on the proximal part" and needed an operation this week.

The relentless men's and women's tennis circuits, which run for 11 months, have come under a harsh spotlight in recent weeks with a string of high-profile players, including Draper, pulling out of tournaments and prematurely ending their seasons.

Several women's players have also struggled with health and fitness concerns in the ongoing Asian swing of tournaments, with the likes of Naomi Osaka, Emma Raducanu, Daria Kasatkina, Elina Svitolina and Paula Badosa all affected.

Draper, who is nursing an arm injury that forced him out of last month's US Open, said physical issues were inevitable in a demanding sport like tennis. His comments came after Rune was left in tears in Stockholm after tearing his Achilles.

"Injuries are going to happen," the 23-year-old Draper said on social media.

"We are pushing our bodies to do things that they aren't supposed to in elite sport.

"We have so many incredible younger guys on the tour right now, and I'm proud to be a part of that.

"However, the tour and the calendar have to adapt if any of us are going to achieve some sort of longevity."

American Taylor Fritz, who won his Six Kings Slam exhibition match in Riyadh on Saturday after Novak Djokovic retired injured, said Draper was right in seeking change.

"Facts. (I'm) also seeing more injuries and burnout now than ever before," the world No 4 said.

"Because balls, courts, conditions have slowed down a lot, making the weekly grind even more physically demanding and tough on the body."

Women's world No 2 Iga Swiatek said the smart option for her amid a grueling schedule would be to cut her commitments for the sake of her health.

Carlos Alcaraz agreed with the Pole, but the men's world No 1 later defended his move to play in the lucrative Saudi Arabia exhibition tournament — where the Spaniard was beaten by Jannik Sinner in the final.