Juan Martin del Potro reveals ongoing challenges in retirement: "I can only walk, I can't even run on the treadmill"

Juan Martin del Potro revealed the extent of the knee problems he is still experiencing, telling La Nacion that he is experiencing pain even during day-to-day activities.

The 34-year-old Argentine, who won the 2009 US Open, retired this season following repeated attempts to come back from a fractured kneecap.

"Today I can only walk, I can't even run on the treadmill, I cannot to climb stairs with no pain, I can't even drive for long unless I stretch my legs because of the pain," he told the Argentine newspaper in an interview given during the US Open, which was published this week.

Having had four surgeries on the knee, del Potro explained that problems with the initial procedure still have to be corrected.

"I am no longer looking for treatments to play Bercy or the Australian Open, and that is a big difference," he said. "I am looking for other doctors and treatments, but so I can climb stairs and not have to hold the railing."

But so far, nothing has worked, and he admits the process has been psychologically difficult.

"I recently went to Switzerland to see another doctor and started a new treatment, one that was recommended to me by several professional tennis players, but so far I haven't had any positive progress," he said. "Every time it fails, it's a very tough blow."

The popular, big-hitting del Potro had injury problems through his career, including problems in both wrists. Along with the Davis Cup, del Potro won another 21 career titles. But being forced into an emotional on-court retirement at the Buenos Aires tournament this season, he's found it tough to get used to no longer being on tour.

"I was No. 3 in the world, until suddenly, I broke my knees and here I am, with nothing," he said.