The 2017 PGA TOUR season has been largely underwhelming for Jimmy Walker, the winner of the 2016 PGA Championship. On Wednesday, we were offered a pretty good explanation as to why. Walker has been diagnosed with Lyme disease.

“Tests taken the Wednesday of Masters week came back positive for the disease, a bacterial infection that infects approximately 300,000 people each year in the United States,” Mike McAllister of PGATOUR.com reported. “Walker thought a couple of weeks ago that he had mononucleosis, but further results confirmed the Lyme disease diagnosis.”

That certainly helps us understand Walker’s slow start to the season. Walker traditionally plays the early year events as well as anyone on tour, with four of his six career wins coming in the first three months of the year.

During the calendar year of 2017, however, he’s played in 10 events and missed two cuts. Walker has recorded five top-25 finishes in those other events, but he has recorded nary a top-five and only one top-10, which came in his first event of 2017.

Despite the diagnosis, Walker is not planning on taking a break from golf.

“One thing he’s hoping to avoid is taking a sabbatical from the PGA TOUR,” McAllister wrote. “He remains committed to playing through whatever issues he must face, and doctors have yet to prescribe rest.”

Walker won his first (and to date, only) career major at the 2016 PGA Championship. He enters the Valero Texas Open as the No. 24 ranked golfer in the world.