“There’s nothing physically wrong with him,” Warthen said. “He feels great.”

Whatever the issue, the Mets have financial reasons to help Niese as much as they can. He is owed $7 million this year and $9 million next year, and he has team options in 2017 and 2018.

In Class AAA, the mere sight of Matz seems to put fear in hitters, some of whom have played in the majors for years. In his 11 appearances, including 10 starts, at the Class AAA level, Matz has compiled a 1.98 E.R.A. and 70 strikeouts.

Matz eases into his delivery, rocks back and then unleashes a 96-mile-per-hour fastball. That power alone makes Viola, a left-hander, jealous. But Matz, 24, can also control his pitches in and out in a way that is beyond his years. When he needs another pitch, he can throw a tight curveball that resembles his fastball as it leaves his hand and “falls off the earth,” as Viola put it, when it reaches the plate. His third pitch, a changeup, is nearly as effective.

Only a handful of left-handed pitchers, Viola said, have had that type of life in their arms. He named Randy Johnson and Clayton Kershaw.

“It took Randy years to command the strike zone with that fastball,” Viola said. “Yes, he had a great slider. But it took him years to be able to do what Steven’s doing now.”

Viola may know Matz better than anyone in the organization. He coached Matz in 2013 with Class A Savannah, during Matz’s first full year back after having Tommy John surgery.

“He was petrified every time he threw a ball, because he was not sure his elbow would survive another throw,” Viola said. “Overcoming that, he realized the little aches and pain he got after pitching wasn’t the end of the world.