Matt Harvey went 13-8 with a 2.71 ERA last season. (Brynn Anderson/Associated Press)

The New York Mets provided just enough information about Matt Harvey to set the Internet off into a frenzy of speculation. What exactly is wrong with the ace pitcher, and will it cause him to miss his Opening Day start on Sunday?

Whatever it is that’s ailing Harvey, the Mets didn’t have much to offer on Monday. “It’s a non-baseball medical issue we have to address,” general manager Sandy Alderson said in Jupiter, Fla. The team was there — minus Harvey — for a spring training game against the St. Louis Cardinals, as it began its final week of exhibition play.

“It came up this morning, as far as I know, and there will be some follow up tests and consultations that will take place over the next couple of days,” Alderson told reporters, adding, “I think it’s a little too early to attach any level of concern.”

Tell that to Mets fans caught between excitement about a pitching-rich team poised to defend its National League pennant and, given their team’s star-crossed history, fear that the other shoe is about to drop at any moment. Those fans have already gone through a bit of a roller-coaster ride with Harvey, who lit up the majors in his first full season, 2013, only to miss 2014 altogether after requiring Tommy John surgery.

The only specific thing Alderson told the media was that Harvey was not seeing an orthopedist about his condition, indicating that it does not involve body parts such as his shoulder, elbow or knee. “I think we need to wait for more medical information before we decide it’s of concern, or great concern, or no concern,” Alderson said.

Harvey is scheduled to kick off the regular season in a World Series rematch with Edinson Volquez, who is set to start for the Kansas City Royals. The pair squared off in Game 5 last fall, with Volquez’s Royals winning that game and their first championship since 1985.

Mets manager Terry Collins said of Harvey’s status (via the Associated Press). “It is mysterious, but I’m not at liberty to discuss it right now. I wouldn’t assume anything until we hear from the doctors.”

Asked if he thought Harvey would be able to make his Opening Day start, Collins said that it was “hard to say right now.” He added, “Certainly what I do know, we’re very lucky to have the pitching we’ve got. In case he can’t go, we’ll have somebody else ready.”

If the Mets need to have another pitcher start on Sunday, they will likely go with either Steven Matz or veteran Bartolo Colon. Of their two top pitchers apart from Harvey, Noah Syndergaard is on a schedule that will have him starting New York’s second game, on April 5, and Jacob deGrom’s wife is expecting to give birth to their first son sometime around the first two regular-season games.

Meanwhile, the Mets are left to try their best to tamp down speculation. “If [Harvey] had to have a wisdom tooth pulled, he wouldn’t pitch tomorrow,” Alderson said (via ESPN). “So let’s not jump to conclusions here.”