Roger Federer's knee injury occurred while he was walking with his twin daughters in a Melbourne park, according to a newspaper in Switzerland.

"Injured walking with his daughters," The Morning declared on its front page.

Federer had previously announced that he underwent arthroscopic surgery this week to repair a torn meniscus, but did not give details other than saying the injury occurred the day following his semifinal against Novak Djokovic at the Australian Open. He described the procedure as successful, and one that would not keep him off the tour for long.

The newspaper also conducted an interview with Finn Mahler, a sports doctor specializing in knee injuries.

"All the kilometers accumulated during the career of a high-level sportsman can cause wear that is the origin of such a tear,” Mahler said. “But a wrong movement of the knee can also be the cause."

Either way, "the age of Federer should not prevent a rapid recovery," he added.

Bruno Waespe, a sports surgeon interviewed by Tages-Anzeiger, told the newspaper that the injury is more common in those older than 30, and while there can be pre-existing damage, it is often caused by a single "rotational movement" that puts undue pressure on the area.

However, he indicated that Federer could be sidelined from competition for more than a month, depending on the extent of the damage.

"There are different types of meniscal tears," he said. "But if it is that only the meniscus is affected and not the cartilage ... Federer could return to competition level in six [to] eight weeks. But specifically, it is important there is no cartilage damage."

The procedure involves a small incision and removal of part of the meniscus, which is then allowed to regrow.

"Although the meniscus takes two [to] three months to regrow,” he added, “and there is still residual pain, he can start casual play again in two to four weeks. But it will take a bit longer till he can go to the limits again."

Federer has withdrawn from scheduled tournaments in Dubai and Rotterdam following the surgical procedure.