Shortstop Jose Reyes sat out Game 1 against the Braves, while third baseman David Wright, center fielder Angel Pagan and left fielder Jason Bay will likely be held out of the nightcap.
""There's fatigue right now on the club," Collins said. "We're tired, there are some tired guys."
Collins said he has noticed his players are worn out lately in the way they are less talkative when he comes out for mound visits, noting that Tuesday's rain-delayed, extra-inning victory against Florida was particularly draining for his players.
While he said that members of the team are both physically and mentally exhausted, Collins said he's confident the team is playing its hardest and not giving away any easy outs at the plate.
"Our guys, they have approached this whole season as professionally as they possibly can," Collins said. "That's why sometimes when you look at a guy, he'll swing at a first pitch and he'll pop it up and you'll say, 'Well, he just gave that at-bat away.' It's unintentional. Certainly the thought process isn't, 'I just want to get out of here and move on. Let's get to the next inning.' I don't think that's the case at all here."