NEW YORK -- Rene Rivera has spent too much time behind the plate not to notice when a pitcher looks awry. The veteran catcher did not so much need to peek at the scoreboard when Noah Syndergaard's velocity began plummeting in the fifth inning Friday, hinting at the arm fatigue that knocked him out of the Mets' 3-1 loss to the Nationals.
"You can notice when you throw 99 and he's at 91," Rivera said. "You can tell right away."
It was a temporarily frightening scene for the Mets, who also learned Friday that Matt Harvey will undergo season-ending surgery, and who lost All-Star outfielder Yoenis Cespedes to a right quad injury earlier in the game. And it was at least a concerning moment for Syndergaard, who is pitching through a bone spur in his right elbow. But the Mets were convinced after the game that Syndergaard was suffering from nothing more than a tired arm -- he referenced it as "a little bit of shoulder fatigue" -- and may not miss significant time.
Syndergaard will, however, skip the All-Star Game presented by MasterCard (7:30 p.m. ET, Tuesday on FOX). He had been one of the top candidates to start for the National League. It was announced on Saturday that Padres left-hander Drew Pomeranz was his replacement on the NL staff.
"It's disappointing," Syndergaard said. "But hopefully there will be a lot more."
Though Syndergaard did not feature his top velocity for much of Friday's start, giving up three runs over his first three innings, he felt nothing particularly amiss until his warmup pitches prior to the fifth. Sensing a lack of life on those throws, Syndergaard attempted only fastballs during his warmup, hoping to rediscover his form. It never came, and by the inning's third batter, his four-seam fastball velocity had dipped to 91 mph -- 10 ticks off Syndergaard's season high.
"It was kind of bizarre more than anything," said Jayson Werth, the batter. "The way they came out just wasn't normal."
In the dugout, manager Terry Collins was also confused, then alarmed once Rivera jogged out to the mound. He followed, with assistant trainer Brian Chicklo by his side. After a lengthy conference, Chicklo walked off with Syndergaard, as reliever Seth Lugo entered from the bullpen.
"I didn't feel any pain," Syndergaard said. "No discomfort. It's just fatigue, really. ... I think it's just that time of the year. It's my first full season in the big leagues. I've thrown a lot of pitches, thrown a lot of innings so far. I just think it boils down to a little bit of fatigue."
After torching his previous career high with 198 2/3 innings between the Minor Leagues, Majors and postseason last year, Syndergaard has thrown 105 2/3 frames this season -- not an atypically high total considering Johnny Cueto leads the league with 131 1/3. But Syndergaard has also spent much of the year battling various stages of discomfort emanating from a small bone spur in the back of his elbow, prompting two MRIs in the past three months.
Though the team stressed that Friday's fatigue had nothing to do with the bone spur, Collins said he expects Syndergaard to undergo a thorough examination on Saturday morning. Even in the likely event that he cannot pitch in the All-Star Game, Syndergaard plans to travel to San Diego to participate in the other festivities.
"I feel like I do a pretty good job of making sure I can go out there every five days," Syndergaard said. "My body's in tip-top shape. It's just a long season. You put a lot of pressure on your body. It's just right now, I think I need a little break."
Anthony DiComo has covered the Mets for MLB.com since 2008. Follow him on Twitter @AnthonyDiComo and Facebook, and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.