Noah Syndergaard Sidelined by Hand, Foot and Mouth Disease. Really.

If the many losses, continual injuries, head-scratching mistakes and personnel changes were not enough to completely demoralize the Mets this season, try this latest development: Noah Syndergaard, two starts into his return from a finger injury, is headed back to the disabled list with hand, foot and mouth disease.

Even in the middle of this eventful season, the Mets could not believe it.

“‘Are you serious?’” Mets Manager Mickey Callaway recalled thinking when he received the news. “I guess it’s very uncommon in adults, period. It’s kind of odd. Maybe it’s the first D.L. stint in baseball with hand, foot and mouth. I don’t know.”

John Ricco, the Mets assistant general manager who is part of the triumvirate leading the team during General Manager Sandy Alderson’s medical leave, announced Syndergaard’s ailment before Sunday night’s game against the Yankees in the Bronx was rained out. Ricco faced 30 minutes of questions from reporters about the clumsy handling of Yoenis Cespedes and his painful feet, the trade of closer Jeurys Familia and the team’s general air of dysfunction.

Then Ricco said he had a final announcement to make: Syndergaard had received a diagnosis of hand, foot and mouth disease, and was expected to miss a start. The team thought Syndergaard, 25, had been exposed to the virus Thursday, when he was helping run a children’s baseball camp in New Jersey. The illness commonly affects children younger than 5 and can be spread through contact.

It was a weekend that seemed to underline the Mets’ reputation as being both deeply unfortunate with their players’ health and remarkably dysfunctional in their front office.

While the Syndergaard news was the most bizarre of the day, much of the focus was still on the much more troublesome developments regarding Cespedes’s feet. He shocked both fans and his own team after Friday’s game — his first after two months away with a hip injury — when he said that surgery would be the only way to address painful calcification in both feet, and that he was unsure if he could last the rest of the season.

“It’s not like he’s been saying this for months and we just haven’t been listening,” Ricco said. “For the first time, to our knowledge, he was considering surgery was when he said that on Friday.”

It was known that the 32-year-old Cespedes — who is in the second year of a four-year, $110 million contract — had dealt with the condition for 15 years, but he said it had gotten worse recently and called it the root cause of his many leg injuries. The recovery time from a potential operation would be 8 to 10 months.

On Saturday, the Mets dealt Familia, one of the most successful relievers in club history, to the Oakland Athletics for two prospects, cash and international bonus pool space. The modest return for Familia raised some eyebrows around the sport, but no Mets executive addressed either significant development, aside from in a news release regarding Familia, until Ricco spoke on Sunday evening.

Ricco, now leading the team along with Omar Minaya and J.P. Ricciardi in Alderson’s absence, explained the silence by noting that he had a prior engagement at home on Saturday and that Minaya had been at Yankee Stadium that night. Minaya was not made available to reporters, Ricco said, because he had not been as involved with the major-league operation until recently. The three executives are being overseen by Jeff Wilpon, the chief operating officer.

Ricco insisted Cespedes and the Mets were on the same page. Even though Cespedes was coming off an extensive rehabilitation stint, Ricco said he had informed the team after Friday’s game that his heels hurt — though Cespedes seemed to portray the situation as much more dire when he spoke to reporters after the game.

Ricco said Cespedes had seen a foot specialist last month during his rehabilitation in Florida. The takeaway was the same as before: shoe inserts, stretching and anti-inflammatories were recommended to allow him to keep playing as long as the pain was bearable.

“Surgery was viewed as down the road, possibly after he’s done playing,” Ricco said.

But then came Cespedes’s statement on Friday. He will be examined by different specialists early this week, and surgery could be an option.

“That’s part of the decision we have to make along with the medical advice: Is it worth shutting him down for that length of time because the bad days are too frequent and too painful for him to continue?” Ricco said.

Ricco also defended the Familia deal. The Mets saved $3 million remaining on Familia’s contract and received two lower-level prospects and $1 million in international amateur bonus pool space. The Mets saved $9 million last season by trading five veteran players on expiring contracts, much like Familia now.

“If we saw a significant return in taking on some of the salary and there was a deal out there like that, there was the ability to do that,” Ricco said.

And then Ricco revealed Syndergaard’s puzzling ailment. The Mets believe the infection was behind Syndergaard’s diminished velocity during his latest start on Friday. Callaway pulled Syndergaard after 84 pitches because he was showing signs of fatigue.

“We knew he was having trouble breathing,” Callaway said. “I put my hands on his legs to talk to him when he came out and I said, ‘Hey man, is everything O.K.?’ And I felt his legs shaking, so he was just weak and run-down, and I think the virus just took its toll.”

Splotches and blisters associated with the disease were also starting to show up on Syndergaard’s hands. He was sent to the doctor and told to stay away from the team to avoid infecting others. Callaway said the team has been keeping an eye on those who had touched Syndergaard on Friday to make sure that they do not show any symptoms.

Syndergaard will be placed on the disabled list on Monday, and the minor league pitcher Corey Oswalt was expected to slide into his spot in the rotation. Ricco said the team expected Syndergaard to make a full recovery in a week or so.

By then, the Mets may have more unexpected twists in a woeful season full of them.