Ahead of this weekend’s first-round Davis Cup tie against Great Britain, John Isner says he isn’t 100 percent healthy. The United States' top-ranked player injured his knee during the first week of January at Hopman Cup, which forced him to retire during his first-round match at the Australian Open.

“I'm getting better,” Isner said. “I wouldn't say I'm exactly where I want to be right now. You know, annoying issue that I'm dealing with, but I'm certainly getting better. I'm not going backwards, so we'll see how these next couple days go.”

Wimbledon champion Andy Murray leads Great Britain in the tie, which will be played on red clay in the outfield of San Diego's Petco Park. Teenager Kyle Edmund could play No. 2 singles for the visitors. Murray may also play doubles with Colin Fleming against Bob and Mike Bryan. Sam Querrey is the U.S.' No. 2 singles player for the tie.

“Well obviously know a lot about Andy Murray on our side,” said U.S. captain Jim Courier. “These guys have seen a lot of him. We don't know as much about the rest of their singles players. We'll learn more as we go over the weekend for sure. It's going to be a challenge for us, because we all know what Davis Cup means to people and what it brings out in other teams. We've experienced some heartbreak at the hands of people that most tennis fans don't know a lot about. So we can't underestimate anything or anyone in this setting. There are three matches that need to go on our side somehow, some way. If we get more than that, that would be great. We're focused on getting three. We know they're going to be tough.”