So Sunday, the Mets put the 27-year-old left-hander on the disabled list with what they officially termed as a left shoulder strain.
Niese was replaced on the active roster by right-handed reliever Buddy Carlyle, who was called up from Triple-A Las Vegas. His spot in the starting rotation will go to Dillon Gee, who the Mets expect to activate off the disabled list in time for Wednesday's game against the Atlanta Braves.
Niese was forced out of his last start after just 12 pitches when he was hit on the side by an Alex Rios line drive. He said after that game that he felt fine, and even that he hoped the Mets would rearrange their rotation to give him two more starts before the All-Star break.
Instead, the Mets told Niese they wanted him to take time off, in hopes of giving a boost to a fastball that has been about two miles per hour slower, on average, than it was the last three seasons.
"There's no discomfort, no pain," manager Terry Collins said Sunday morning. "We're just seeing a decrease in stuff. You don't need radar guns to tell you there's something going on here."
The decrease in velocity hasn't been reflected in Niese's results. His 2.96 ERA is the best in the Mets rotation and among the best in the National League.
But with Gee ready to return from the DL, after missing nearly two months with a strained right lat, the Mets had a decision to make about their rotation. They decided that the best course would be to give Niese a couple of weeks off, in hopes that it would strengthen him for the second half of the season.
"Last year when he rested his shoulder, the second half was huge," Collins said. "His second half last year was outstanding, after we took time to get his strength back. I told him, 'You'll have 15 starts left, go win 10 of them.'"
Niese declined to comment when approached by reporters Saturday night, and wasn't available to comment before the Mets' Sunday game against the Texas Rangers.