"There's a little concern there, but we also know when he gets back to what we expect or what we have seen, he's dangerous," Collins told reporters before the Mets' 5-0 loss to St. Louis on Tuesday.
"This is all new to us because this guy has not struggled since he's been here," Collins later added. "So we've got things we've got to work on."
Cespedes injured his hip while trying to make a diving catch during Saturday's game against Colorado -- the latest malady in an injury-riddled season. He returned from the disabled list on June 10 after missing six weeks with a strained left hamstring.
In his past 15 games, spanning 72 at-bats, Cespedes has one RBI -- from that solo home run June 23.
"Obviously, power is huge from the legs," Collins said. "Just looking at the swings, the lower half seems to be fine. He's just not getting the bat out in front. He's getting beat on some balls in. I don't know if that has anything to do with the lower half because I think that's still intact, but I can't say it isn't. He hasn't complained about it. He's just not getting the bat to the baseball where he normally does."
Collins said he has tried to remain supportive, and he's sure Cespedes will get it going eventually.
"He was swinging very, very well going into the break. I talked to him today and I said, 'Look we may make some changes here down the road, but get 'er going,'" Collins said.
"... I'm not sure he's ever been through anything like this before in his whole career. ... You've just got to keep grinding it out, keep working at it. ... He's trying to get himself undone and get it going and when he does he'll start to carry us again."