LONDON—Less than two weeks before the start of Wimbledon, top American man No. 1 John Isner said he isn’t putting pressure on himself, nor is he "desperate" to achieve a second Grand Slam quarterfinal.

Isner reached the last eight at a major for the first and only time at the U.S. Open in 2011. He has gotten past the third round just once since then, at last year’s French Open.

After a promising build-up to this year’s French Open—Isner lost only to Rafael Nadal, Tomas Berdych and the eventual champion in Nice, Dominic Thiem—the 30-year-old fell in the second round at Roland Garros to Jeremy Chardy.

"I’m not desperate to get that [second Grand Slam quarterfinal]," the world No. 18 said at the Aegon Championships in London. "I certainly believe I can get there. The results in the Grand Slams have been a bit disappointing since that first quarterfinal, but I’m not putting pressure on myself to get back to the quarterfinals or get back to the second week of a Slam.

"I feel I’m under the microscope a little bit as the No. 1 American. People can say what they want to say about American tennis, I catch the brunt of a lot of it, being the No. 1."

Following the French Open, Isner went home, where he "relaxed" and "regrouped." He then hit the gym and practiced hard.

"It was super hot in Florida," he said. "I’m happy to be [in London] now. But I did play well on clay. The match I lost at the French Open, I’d have beaten a lot of people that day. Jeremy played well."