On Sunday the Celtics announced Hayward is in the concussion protocol and is doubtful for Monday's game against the Nuggets while Horford is probable.
Horford, who left the game in the third quarter after banging knees, was eventually able to return for the fourth. It was a reminder of why the Celtics already had stated it was a priority to get the 12th-year center rest before the end of the regular season.
And, after Saturday's win, coach Brad Stevens reiterated that desire.
"We have three or four games already picked out over the next 12 that Al will not play," Stevens said postgame. "So if he feels like tomorrow he doesn't feel good, he won't play Monday.
"We'll make sure that we manage that over the course of time. He's felt great all the way through -- it's the first time this has come up. And so, that's why I didn't want to put him back in. For whatever reason, he felt better in the fourth. He came up and said he wanted to go in."
Horford missed several games in November and December with knee tendinitis, which slowed him in the early going. But he has consistently been playing at the level he was prior to this season over the past couple of months -- which has only reinforced his importance to Boston. The Celtics need to make sure he's ready to go for the postseason, where the likes of Joel Embiid, Marc Gasol, Brook Lopez and Myles Turner await in the Eastern Conference playoffs.
"I think it's just the amount of games that we've been playing at the level that we've been playing," Horford said, "and just making sure that I'm at my best and we are all at our best come playoff time."
Hayward, on the other hand, left the game in the first half with a strained neck after he collided with Hawks forward John Collins early in the second quarter. He was ruled out a short time later with a strained neck, and Stevens said after the game Hayward had been sent home before the game had ended.
"I talked to him at halftime," Stevens said. "Obviously, pretty woozy from that hit. I don't have any update on him, but you could see right away that it was quite a hit."
It remains unclear if Hayward will be ready for when the Celtics next play -- Monday night against the Denver Nuggets -- when Isaiah Thomas could make his first appearance at TD Garden since being traded for Kyrie Irving 18 months ago.