Celtics coach Brad Stevens said the team is investigating how Smart, who went to a hospital to get stitches, injured himself on Wednesday afternoon.
"He lacerated his hand on glass in the hotel, got stitches. I don't know the full story," Stevens said before the game. "We're learning more about that. [Assistant general manager] Mike Zarren and [assistant athletic trainer] Brian Dolan were with him at the hospital two hours ago [when Smart] got stitches. It doesn't sound like a long-term injury, but we're doing more research on how it happened."
Pressed on why the team was investigating the incident, Stevens added, "Obviously, I want to make sure that I'm thorough in telling you how it happened and what happened. But, again, I think that he cut his hand in the hotel on glass sometime this afternoon."
Horford, who has endured two concussions over the past two seasons, was examined by Lakers doctors on Tuesday and did not exhibit concussion-related symptoms.
Stevens and Horford said the Celtics were simply being cautious in the immediate aftermath to ensure Horford remained asymptomatic.
"We're going to just observe him [Wednesday]," Stevens said of Horford. "He'll be out. We just want to make sure, and make sure he's symptom-free before letting him get back out on the court. And I think that, obviously, having one [concussion] earlier in the year and having one last year, I think it's the right move."