After sitting out the second half of Saturday’s win in Toronto with an illness, Jordan Walsh will not play Monday against the Indiana Pacers.

The Celtics ruled the 21-year-old wing out for its matchup with Indiana at TD Garden. Jaylen Brown (illness) was upgraded to available after missing Saturday’s 112-96 victory over the Raptors.

Walsh has been a surprise standout for Boston this season, starting the last 16 games and posting career-best numbers in every statistical category. He’s averaging 7.6 points, 5.0 rebounds and 1.2 steals per game while shooting 58.4% from the field and 44.4% from 3-point range.

Head coach Joe Mazzulla said Walsh’s off night on Saturday (zero points, four rebounds, minus-15 in 13 minutes) was the result of his illness. Walsh watched the second half of the win over Toronto from the bench.

“He was sick today,” Mazzulla told reporters after Saturday’s game. “He wasn’t supposed to play, but we pushed him to and wanted to see what he could give us. He gave us what he could … but he just obviously wasn’t at his best.”

The Celtics are 12-4 since Mazzulla elevated Walsh to the starting lineup in mid-November.