deGrom will probably miss his next two starts, Collins said. Matz has an outside chance of pitching again this season.
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deGrom is on anti-inflammation medication to eliminate soreness in his right forearm and has been told to rest until well into the coming week. Matz has a tender left shoulder and was sent to Florida on Sunday morning to begin his rehab under controlled circumstances.
"I haven't thrown a ball yet," Matz said as he was about to leave the team on Saturday night. "No long toss, no catch, no nothing. That's what I'm going to start doing down there."
Collins said it will be weeks before the Mets are able to make a determination on a potential return for Matz, who hasn't pitched since Aug. 14.
"We're hoping that it will be well before that," Collins said of deGrom, who made his last start on seven days' rest but completed just five innings in that game, a loss to the Marlins on Thursday.
deGrom has allowed 16 runs on 31 hits and seven walks in his past three starts, posting a 9.82 ERA over 14 2/3 innings in that span.
In the worst-case scenario, Collins is well aware that he may have seen the last of Matz and deGrom for the remainder of the regular season. Still, the Mets aren't quite there yet.
Right-hander Matt Harvey is already out until 2017 after losing feeling in his right arm and right fingers because of a compressed nerve. He had a rib removed to address thoracic outlet syndrome and hasn't pitched since July 4.
On Thursday, deGrom allowed three runs on six hits, walking four, striking out six and throwing 102 pitches. He looked all evening like he was struggling with his command and control, uncharacteristically falling behind most Marlins hitters.
When he walked off the mound, deGrom signaled the Mets' trainers, and unbeknownst to his manager at the time, told them he was having arm issues. An MRI exam on Friday revealed no structural damage.
Still, deGrom, Matz and Harvey are three-fourths of the postseason rotation that pitched the Mets into last year's World Series, where they lost to the Royals in five games.
So don't blame Collins if there are anxious days ahead as he awaits further news on deGrom.
When asked where deGrom is in his recovery, Collins said:
"He's resting now. We wanted him to rest and to take four days of some medicine to see if we can calm this down. Probably Wednesday we'll start to see where he's at, and we'll go from there."
For his part, deGrom was wandering around the clubhouse on Sunday like a little kid looking for something to do.
deGrom claimed he "felt good" when asked about his condition.
Obviously, this is not where Collins wants to be so late in the season with so much on the line. He has a healthy Noah Syndergaard and Bartolo Colon, followed by rookies Seth Lugo and Robert Gsellman, and young righty Rafael Montero. The latter three have combined to make six Major League starts this season.
All have contributed well as the Mets have made a spirited run for the NL's second Wild Card spot, climbing from 5 1/2 games back to only 1 1/2 games out heading into their game on Sunday night.
But Collins knows that the Mets will go only as far as their starting pitching will take them. And two more times through the rotation with the current alignment of starters is going to eat up 40 percent of the remaining schedule.
Looking on the brighter side, the Mets continue to develop Major League-caliber pitchers who can fill in when circumstances on the big league club are dire.
"I credit our Minor League staff with keeping these guys coming," Collins said. "We made so many trades last year where we lost such quality pitching, you weren't sure what was left. I'll tell you what, there are still some good arms coming. We've asked them to step up, and they've stepped up.
"You can only create opportunities when you're going through what we're going through. The players have to decide: 'Here's my chance.' They've done a great job since they've been up here."
The question is whether that will continue.