a mild case of mononucleosis.
Roddick said on Saturday that one of several blood tests came back positive for mononucleosis. Doctors told him he's probably had it for the last couple of months and should be nearly over it.
"I'm just glad that we found out something that was causing it," said Roddick, who is getting ready for next week's Cincinnati Masters. "It's weird, the fear of kind of the unknown and not knowing what's going on. There were some days where it was good, and some days where it was real bad. So it was like you would have one of those two or three good days, and it was like, 'OK, you're just being kind of a wimp.'
"So it's nice to have a little bit of clarity moving forward. It's not something that's going to affect me, anything super-serious."
Roger Federer had mononucleosis in 2008, leading to a decline in his wins and his ranking. Roddick has slipped to No. 11 in the world while struggling through a summer of out-of-character losses, making him wonder what was wrong.
Seeded fifth at Wimbledon, he lost to 82nd-ranked Yen-hsu Lu of Taiwan in the fourth round. He lost to Gilles Simon in the third round at Washington on Aug. 6, saying afterward that he didn't feel right. He got blood tests in Washington and more in Texas, and withdrew from the Rogers Cup in Toronto this week while awaiting results.
"I guess I've been dealing with a mild, mild case of mono for the last couple of months that I wasn't really sure about," he said. "So they think I'm fine now. They think I'm most of the way through it, if not all the way through it."
Roddick said he tired more easily this summer, prompting him to cut back on his workout schedule.
"I enjoy training all day and running all day long and doing all that stuff," Roddick said. "You know, I opted out of probably four or five workouts this summer — that I've never done before. So that wasn't fun. It was just me wondering if I was out of shape or what was going on, why there was this lethargic feeling."
He expects to be fine for the U.S. Open, where he lost to John Isner in the third round last year. Roddick won the 2003 U.S. Open. He said his doctor was encouraging.
"He said, 'You know, the good news is you're probably ready to rock. Be a little careful, but you should be fine to go,'" Roddick said. "That was a relief."