Jaylen Brown sat out against the Knicks with left Achilles tendinitis — the same injury that ended Tatum's season last May.

Jaylen Brown was a late scratch from Thursday's matchup against the Knicks at Madison Square Garden with left Achilles tendinitis. The injury is particularly alarming because it mirrors the same Achilles issue that ended Jayson Tatum's season last May, keeping the Celtics' other star out for months.

Brown had scored 35 points just the night before, showing no visible signs of the issue. The sudden nature of the setback has raised concerns about the Celtics' durability heading into the postseason. Without Brown, Boston fell 112-106 to the Knicks, failing to clinch the Atlantic Division crown and the #2 seed.

The Celtics are walking a tightrope. Tatum just returned from his own Achilles rehab and looked good with 24 points, 13 rebounds, and 8 assists against New York, but having both stars dealing with Achilles issues is a nightmare scenario for a team with championship aspirations. If Boston has to manage Brown's minutes or — worst case — shut him down, their ceiling drops dramatically.