Hayward is getting the night off for the second game of a back-to-back as he continues his comeback from last season's left ankle injury.
Stevens said the team's medical staff decided Hayward should rest after he experienced general soreness in his ankle following Friday's 113-101 loss to the Toronto Raptors. Stevens said the team isn't "overly concerned."
"Just had a little soreness this morning, nothing big," Stevens said.
Stevens added that there are no plans in place to rest Hayward regularly on the second night of back-to-back games.
"That would be something that they'll take game-by-game, night-by-night," Stevens said.
Hayward played 24 minutes and scored 14 points on 6-of-13 shooting Friday. He is currently restricted to playing 25 minutes or fewer.
"I felt like I found a little bit of rhythm there in the second half," Hayward said after the game. "It was a good start for me. Each game will be progress."
Still, it wasn't all good for Hayward, who suffered a gruesome left ankle injury five minutes into last year's season opener and missed the rest of 2017-18.
"There's times where it still feels like I'm not playing like myself. I'm thinking too much out there," Hayward said. "I felt like I was doing that in the first half a little bit."
After the Knicks game, the Celtics next play Monday against the Orlando Magic.
ESPN's Ian Begley and The Associated Press contributed to this report.