SAN FRANCISCO -- Three hours before Thursday's series opener at AT&T Park, New York Mets pitching coach Dan Warthen entered the visiting manager's office and relayed the latest injury news to Terry Collins.

Steven Matz was experiencing shoulder discomfort, prompting the Mets to scratch him from Friday's game against the San Francisco Giants. Matz is being dispatched to New York for an examination with team doctors Monday.

"You guys walked out and Dan walked in," Collins said, referring to a pregame media session breaking up. "I went, 'You've got to be kidding me.' "

The Mets' celebrated young rotation is a shell of the hype these days. Matt Harvey underwent season-ending surgery July 18 to address thoracic outlet syndrome. Matz, already diagnosed with a bone spur in his pitching elbow that will need to be surgically removed after the season, awaits a more firm diagnosis about his shoulder. Jacob deGrom and Noah Syndergaard both rank in the top seven in the National League in ERA but are not as intimidating as a year ago. And Zack Wheeler has suffered three setbacks this year in his comeback from Tommy John surgery and now appears likely to miss a second straight full season.

Collins said he had been warned by a host of baseball men, including Giants manager Bruce Bochy and Hall of Famer John Smoltz, that this could happen. By reaching the World Series, the Mets played until Nov. 1 last year.

The young starting pitchers have been hit particularly hard as their bodies have not responded this year.

What has gone wrong? Is it a really hangover from the 2015 workload? Bad luck? Both?

"That is a really legitimate question," Collins said. "When we get together with our coaching staff, we ask the same questions. I think it's a combination. I've said it before. People don't want to hear it because they think it's an excuse. We don't make excuses here. But I've had too many guys that have managed in the postseason, deep into the postseason, tell me there's a residual effect. And a lot of times it's your pitching.

"Guys have accumulated a lot of innings -- and pressure innings, not just innings. We're talking about the last two months of last season, these guys had to pitch big games every night. The side effect on the next year is your body -- not necessarily the muscles, but the adrenaline -- just beats your system up."

There's a reason beyond quirkiness that the Giants win the World Series in even years, then take a step backward the following season.

"I talked to Boch about it [Thursday] -- exactly that," Collins said. "He told me last winter, 'You're going to see some effect from this, from playing into November.' I didn't know what he meant, to be honest. And then I talked to John Smoltz. And he said the same thing.

"That's why we talked about trying to take it easy early in the spring, to build these guys up. We tried to do that. We kept them around 100 pitches for, heck, almost two months. And then said, 'OK, we can start to let them get deeper into games.' I think it's helped a little bit, but I think you're still seeing the fact that there's a residual effect of playing that deep, and we've just had some bad luck."

Syndergaard, who starts opposite Jeff Samardzija on Sunday night, has struggled to put away batters of late. Over his past six starts, he has averaged 18.8 pitches per inning. That has resulted in an average outing length of 5⅔ innings during that span.

Meanwhile, DeGrom is coming off an outing in which he gave up career highs with eight runs and 13 hits Thursday against the Giants.

The Mets initially had contemplated using Monday's day off to skip fifth starter Jonathon Niese and keep the other pitchers on standard rest. Collins has abandoned that consideration, however, because of Matz's shoulder issue and deGrom's struggles in his last start. Niese is the latest to hold the rotation spot originally occupied by Harvey. Logan Verrett went 0-3 with a 7.18 ERA in seven starts in that role before being demoted to Triple-A Las Vegas.

Despite Niese's 9.28 ERA since joining the Mets in a trade with the Pittsburgh Pirates, he will start Tuesday's all-important opener at Busch Stadium. The Mets are chasing the St. Louis Cardinals for the second wild-card spot. Matz is lined up for the third game of that series, but it's unclear if he will be healthy enough to pitch by then, which means the Mets might be forced to use rookie Seth Lugo. DeGrom starts Wednesday on extra rest, rather than Tuesday in the opener, which would have allowed the Mets to skip Niese.

"Not that Jake's hurt, but [Thursday] night may be a perfect example of their fumes are starting to run a little low," Collins said.

The Mets did enter Saturday's game with a 3.63 ERA among their starting pitchers. That still ranked third best in the majors. But they're limping to the finish line this year as the rotation's 2015 workload and injury misfortune catches up with them.