Kristaps Porzingis warmed up at Madison Square Garden ahead of Saturday’s Celtics-Knicks matchup. But minutes before tipoff, the team announced their starting center would not play.

After announcing him as part of its starting lineup, Boston ruled out Porzingis with what the team called a non-COVID illness.

The Celtics already were down one starter in Jrue Holiday, who missed his second straight game with a right shoulder impingement. Newly signed reserve wing Torrey Craig also was inactive as he continued to recover from the ankle injury that’s sidelined him since Dec. 30.

Al Horford and Luke Kornet started against New York in place of Porzingis and Holiday.

Porzingis has been one of Boston’s top performers since the start of January, averaging 20.6 points and 7.6 rebounds per game over his last 15 appearances while shooting 45.2% from 3-point range.

The Celtics dealt with a similar situation during their Jan. 18 loss to Atlanta. Porzingis was inactive for that game, and Horford was removed from the starting lineup just before tipoff. Kornet stepped in as a starter and played well, finishing with 17 points, seven rebounds, four assists and two steals, but Boston lost 119-115.

The Knicks ruled out starting forward OG Anunoby (foot) for Saturday’s contest. All-Star big man Karl-Anthony Towns (knee) was active for New York after being downgraded to questionable earlier in the day.