NEW YORK -- As the bottom of the fourth inning unfolded on Wednesday at Citi Field, rumors bubbled throughout the Mets' dugout. Paul Sewald was warming in the bullpen, preparing to replace Jacob deGrom in a scoreless ballgame, and nobody seemed to know why.
"Usually, you see something [happen]," third baseman Todd Frazier said. "It's just one of those freaky things where you can't explain it."
By the end of their 7-0 loss to the Braves, the Mets could at least explain the what and the how, but not much more.
Batting in the third inning, deGrom hyperextended his right elbow on a swing, wincing in pain but ultimately staying in the game. After pitching a scoreless fourth, he returned to the dugout and alerted manager Mickey Callaway of his pain.
The conversation went something like this: deGrom told Callaway that he felt pain while swinging but could pitch without issue. Callaway told deGrom that he was done for the day and handed him off to the training staff, which sent deGrom for an MRI.
The Mets don't anticipate knowing the results of that test until Thursday morning.
"I'm sure I won't sleep very good," Callaway said. "He's a big part of our team. But when all is said and done, whatever happens, we can sit here and worry about it and cry about it or whatever, but that's not going to do us any good. Somebody's going to have to step up if we get some bad news."

Because deGrom was at the hospital undergoing tests, he was unavailable to comment.
Cruising through the early innings, deGrom struck out the side in the third inning and six total, allowing just two hits and lowering his ERA to 1.87 in seven starts. But he descended into the clubhouse tunnel following the top of the fourth, and did not return to the field.

The initial diagnosis was a hyperextension, a rare injury for a pitcher. Among Mets position players who have hyperextended their elbows in recent years, Lucas Duda missed about five weeks in 2017, and Travis d'Arnaud sat for about the same amount of time two years prior. Juan Lagares hyperextended his throwing elbow in September 2014, then had the entire offseason to recover.
In the immediate aftermath of deGrom's injury, Callaway made it clear that he wouldn't speculate how much time the right-hander might miss, but he has at least begun considering potential replacements. Two pitchers Callaway mentioned were Corey Oswalt, a rookie who has thrived in both the Majors and at Triple-A Las Vegas this season, and Matt Harvey.
The latter has allowed two runs in four innings since being demoted to the bullpen last week, prompting team officials to say he must earn his way back to the rotation. Regardless, as deGrom descended into the clubhouse tunnel, Harvey's name "popped into my head right away," Callaway said.
"We do need to have that discussion," Callaway said. "Is it better off for our team, better off for Matt Harvey to stay down there longer? So we'll just have to talk through that."
Whoever replaces deGrom will have a difficult time emulating one of the National League's best pitchers. Riding one of the best runs of his career, deGrom has 54 strikeouts and 11 walks in 43 1/3 innings, the last 18 1/3 of which have been scoreless.
Although health issues -- specifically, a 2010 Tommy John surgery -- prevented deGrom from debuting in the big leagues until a few weeks prior to his 26th birthday, he has mostly stayed on the field since then. Minor bouts of elbow and shoulder soreness cost him time early in his big league career, and he underwent surgery late in 2016 to reposition a nerve in his right forearm. He responded with the most durable season of his career, setting career highs in 2017 in starts, innings and strikeouts.
"It's the last thing we want to see, one of our guys come out," outfielder Jay Bruce said. "Obviously, Jake is one of the main cogs here on the team and for the rotation. He really sets the tone for us. When you see him come out of the game, there's concern. You just hope he's fine."