It all started with a headache.

No big deal, Scott Kingery thought. But then came the chills and a fever so high that he couldn’t move a muscle during a mostly sleepless night at his home in Phoenix. A few days later, the Phillies’ 26-year-old second baseman lost his senses of taste and smell, all while dealing with fatigue and shortness of breath that lingered for weeks.

“In my mind, I was thinking, ‘OK, does it get worse than this?’” Kingery recalls. “At the time, I had no idea what was coming next.”

Kingery spoke from a room in the Phillies’ clubhouse on Saturday, exactly one month after that seemingly innocuous headache, eight days into training camp, and the first day that he was able to join his teammates since overcoming COVID-19 and clearing Major League Baseball’s myriad health-and-safety regulations.

Let Kingery serve as a cautionary tale, then, for the insidiousness of the coronavirus even on young, physically fit professional athletes and how much disruption it could cause in MLB’s attempt to get this 60-game season off the ground – and keep it going once it starts.

"It's not just a two-week thing," Kingery said. "I think there's some stuff with the testing that [shows] the virus can stay in your body for a lot longer than we think. Because of all the protocols you have to go through, it's been about a month-long thing. That's going to be half of the season if you get it during the season."

» READ MORE: Coronavirus driving Phillies’ plans for starting pitching rotation

Kingery took batting practice and fielded some grounders on Saturday. But he didn’t participate in an intrasquad scrimmage at Citizens Bank Park and cannot say for certain that he will be ready for the July 24 season opener against the Miami Marlins.

"I'm just going to need to get in there in a live game and feel it out a little bit," he said.

That could take several more days. It wasn’t until Wednesday, after all, that Kingery was allowed to travel to Philadelphia.

Per MLB’s protocols, Kingery had to test negative for COVID-19 twice within 24 hours and be fever-free for at least 72 consecutive hours. His second negative test came back Wednesday afternoon. A few hours later, he hopped a red-eye flight, and within a few hours of landing, he was in a doctor’s office for additional testing, including an electrocardiogram to make sure the virus didn’t damage his heart.

But at least Kingery, one of three Phillies players known to have tested positive for COVID-19 (with reliever Tommy Hunter and outfielder Mikie Mahtook) went through all of this before the season. When a player contracts the virus during a season that will last only 66 days, it could take him out of action for half the schedule.

“That could be upwards of around 30 games,” pitcher Jake Arrieta said. “That’s a tremendous hit for any team, especially if it’s a guy that we count on to be in our lineup every night or one of our starting pitchers. It’s going to be tough. I don’t mean to be pessimistic, but I feel like it will happen at some point.

“It was scary to see Scotty get it; it’s scary to see [Atlanta Braves All-Star first baseman] Freddie Freeman get hit really hard the way he did. If it can happen to them, it can happen to any of us.”

» READ MORE: Phillies manager Joe Girardi on players possibly kneeling for national anthem: ‘Whatever they do, I support what they do’

Kingery believes he contracted the virus from someone in his workout group during baseball's hiatus. He had a trainer come to his house and was working out with several players in the garage, which seemed to him to be a sensible way to quarantine and stay in shape at the same time.

"But there were still risks," Kingery said, "and I wasn't able to say exactly where everyone that I was with was going after those workouts."

If Kingery isn’t ready for opening night, the Phillies have a few second-base options.

Veteran infielders Josh Harrison, Logan Forsythe, and Neil Walker have extensive experience at the position but would need to be added to the 40-man roster. Forsythe and Walker may choose to opt out of their minor-league contracts on July 18 if they aren’t informed that they will make the season-opening roster, or receive a retention bonus to stay as minor-league depth; Harrison can opt out on July 18 but isn’t eligible for the retention bonus.

Manager Joe Girardi said Jean Segura likely will remain at third base even if Kingery isn’t ready.

» READ MORE: J.T. Realmuto says Phillies’ contract negotiations haven’t ‘gone anywhere’ since March

“Scott’s health is the most important thing, and I don’t want him to end up on the DL because his legs weren’t ready or he’s still feeling a little bit weak,” Girardi said. “We’ve got to make sure that he’s really good to go. And those guys [Harrison, Forsythe, and Walker] give you a lot of options.”

It’s all virus-permitting, of course. And as Kingery can attest, COVID-19 can’t be taken seriously enough.

“I think every team understands that, at this point, you’ve got to wear your mask as much as possible,” Kingery said. “Because if one guy in the clubhouse gets it, you don’t know who they’ve exposed to the virus, and we don’t know who’s going to have to quarantine if something like that happens.

“If you can just take as many precautions as possible to stay safe and keep your distance from others, that’s the best way to kind of keep yourself from getting the virus.”