Jaylen Brown is out tonight vs.

Jaylen Brown has been ruled out of Thursday night's marquee matchup against the Knicks with left Achilles tendinitis. It's an injury that's been nagging him for weeks, and with the playoffs starting April 18, the Celtics are right to be cautious with their star wing.

Brown is having the best season of his career — 28.8 points, 7.0 rebounds, and 5.2 assists per game. He's been the engine that's kept Boston in contention for the 2-seed in the East. Without him tonight, the Celtics will lean on Jayson Tatum and Derrick White to try to clinch the Atlantic Division crown and lock up home-court advantage through the Eastern Conference semifinals.

The bigger concern isn't tonight — it's whether this Achilles issue lingers into the postseason. Achilles tendinitis is the kind of injury that doesn't just go away. If Brown can't go at full speed in a seven-game series, Boston's championship window gets a lot smaller.