Harvey took a liner directly on his right arm off the bat of Cubs center fielder Dexter Fowler in Saturday night's 4-2 win in Game 1 at Citi Field, and there was more swelling than expected in his tricep two days later.
Collins had indicated on Sunday before the Mets made it 2-0 in the best-of-seven series that Harvey was on track to make the Game 5 start. Then he took a look at Harvey's arm.
"He's pretty sore and pretty swelled up," Collins said. "As we sit here today, he's still a go. But that could certainly change in the next couple of days. He's here to get some treatment. I mean, I was pretty surprised at how swelled up it was [Sunday]. So we really are going to keep an eye on it the next couple of days."
Game 3 is Tuesday night with a 7:30 p.m. ET air time, 8 p.m. game time on TBS, with right-hander Jacob deGrom on the mound for the Mets. Rookie lefty Steven Matz is slated for Game 4 on Wednesday night.
Harvey was on the field for Monday's optional workout and had a light catch.
"He just came out to throw," Mets pitching coach Dan Warthen said. "A lot of guys hate to have a day off, so a lot of players come in on a day off and just play catch. He's doing his treatment. I saw him in there. The doctors looked at it [Sunday]. He's in great shape, great spirits."
Collins said he hasn't decided yet who might start if Harvey is sidelined.
"We don't know yet," Collins said. "We obviously have alternatives with Bartolo [Colon] and Jon [Niese]. So if we need to put a spot starter in there, we certainly have them."
Colon, a 42-year-old right-hander, won 14 games this season as a starter and has been in the bullpen so far this postseason. Niese, a left-hander, struck out lefty-swinging Anthony Rizzo to end the sixth inning with a runner on second in relief of Noah Syndergaard on Sunday night.
Warthen, though, seemed far more optimistic about Harvey's availability than Collins.
"He's got a triceps for the first time in his life," Warthen said. "He really thinks a horse kicked him back there. But Matt is on board 100 percent. Ever since that incident, he wants to pitch. He wants to pitch when it's his turn. He wants to finish this season. He wants to finish the next season."
On the play in question, Harvey picked up the ball after the Fowler smash and threw him out at first base to open Saturday night's top of the sixth inning. Mets trainers and Collins went to the mound to see if he was hurt, but when Harvey was able to freely toss a few warmup pitches he remained in the game until Kyle Schwarber homered with one out in the eighth.
Collins had said that Fowler hit the ball so hard that it left stitch marks on Harvey's triceps. But he hadn't anticipated so much swelling in the aftermath.
"Any time there's swelling, it leads to stiffness," Collins said. "So as stiff as he was [Sunday], we're going to be careful."
Harvey allowed two runs on four hits with a pair of walks and nine strikeouts, bringing his postseason record to 2-0. He threw a shaky five innings in a 13-7, Game 3 victory over the Dodgers in the NL Division Series and was credited with the win.
Harvey's been on an innings count all season and has now thrown a total of 204 innings. How much he would throw, particularly down the stretch, became a point of contention and Harvey made only five starts during the last month of the season.
"I don't think it's going to affect him down the road," Collins said, "but down the road is still three days away. So we'll just have to see how he is. I think the big time will be [Tuesday] because that would be the day he throws [in the bullpen] anyway. So we'll have to make our judgments on how he feels [on Tuesday]."