Earlier this week, Mets officials insisted there was value in Santana making a few more starts in his first season back from left anterior capsule shoulder surgery. But the left-hander's back stiffened following his last outing, then again after a routine bullpen session earlier this week.
That prompted an MRI, which revealed inflammation surrounding a disc in his lower back. Not wanting to risk further injury to his back, shoulder or ankle, the Mets shut Santana down for the season.
"I wanted to keep pitching," Santana said. "It's too bad that I have to go down like this, but it's part of the game."
If nothing else, Alderson and company deemed it a successful season for Santana given the health of his shoulder. Manager Terry Collins said in March that he would be thrilled if Santana started 25 games, and the lefty nearly achieved that feat with 21. But after jumping out to a 3-2 record and 2.38 ERA over the first 11 of those games, culminating with a no-hitter June 1 against the Cardinals, Santana went 3-7 with an 8.27 ERA the rest of the way. He spent time on the disabled list with a sprained right ankle and was 0-5 with a 15.63 ERA over his final five outings.
"We've tried to make it really clear that in the big scope of things, this has been a very positive year for him," Collins said. "He's made it through a surgery that nobody thought he could. He's healthy. He's got a tweak in his back, but with rest and exercises, it will go away."
Unlike Alderson and Santana, Collins acknowledged the possibility that leaving the left-hander in for 134 pitches during his no-hitter may have altered the course of his season. But because Santana's shoulder is still intact, the Mets do not believe his current injury -- regardless of cause -- will have any effect on his long-term health.
The short-term consequence is that Santana is out of the rotation, though certainly not for good. The two-time Cy Young Award winner is under guaranteed contract for one more season at $25.5 million, and has a $5.5 million buyout on his $25 million team option for 2014. The justification for shutting him down now is that he can presumably open next season healthy. Because surgery is not necessary, Santana will be able to enjoy a rehab-free offseason for the first time in three years.
"Now that I'm going to rest and let me body heal, I think I'm going to be fine," Santana said. "My mindset is to be ready to go from Day 1."
But there is some question as to his durability heading into his age-34 season. Since joining the Mets in 2008, Santana has undergone surgeries on his left elbow, right knee and left shoulder. His only full season came in his first summer with the Mets, though the team is banking on a quiet offseason altering that trend.
"Because of what I've seen this year," Collins added, "I know we're going to have a good pitcher with some rest."
In the interim, McHugh will make his Major League debut. Skyrocketing up prospect lists with a dominant 12-start stretch at Binghamton earlier this year, McHugh went 2-2 with a 2.45 ERA, 52 strikeouts and 19 walks over his final nine outings for Triple-A Buffalo. He will be on regular rest for Thursday's start.
"It was a little bit of a surprise, for sure," McHugh said of his promotion. "We thought maybe when September rolls around, but it's a little earlier than that."