LONDON—Juan Martin del Potro says he is confident that his backhand will eventually return to its normal level, but he does not know when that will happen.

The Argentine, who upset fourth-seeded Stan Wawrinka in the second round of Wimbledon, is largely slicing the shot, and he hit about 95 percent of his backhands crosscourt during the match.

"The doctor says, 'You can do it,’” Del Potro said, adding that part of it is mental. “…But he doesn't know when. I have to deal with a lot of stuff on my mind. But I think just two or three months ago I only play slices, and now sometimes I hit with topspin. On the returns, I can go harder. That is a small thing to me, but it's important."

Del Potro has had three procedures on his left wrist and has played only intermittently since returning to the tour this season. He has indicated, however, that he will begin playing a full schedule from here on out.

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He spends two to three hours a day rehabbing the wrist.

“That's why I'm [keeping] positive and working hard on that shot, because I know I'm in a good way to get better as soon as I can,” the former U.S. Open champion said. “But sometimes the wrist needs time to [recover] completely."

In the meantime, he is taking advantage of the low bounces at Wimbledon.

"I'm playing too much slices," he said. "But on this surface, that is a great game to do it, because the grass [helps] me a little bit when I hit slices or when I came to the net."

Del Potro is a former semifinalist at Wimbledon.