Defensemen Jacob Trouba (upper body) and Ryan Lindgren (upper body) also will not play again this season. Left wing Chris Kreider remains day to day with a lower-body injury.
The Rangers were eliminated from Stanley Cup Playoff contention Monday.
Panarin was injured at 7:40 of the second period when he was thrown to the ice by Washington forward Tom Wilson during a post-whistle altercation near the Capitals net.
Wilson was assessed a double-minor for roughing and a 10-minute misconduct. He was fined $5,000, the maximum allowable under the Collective Bargaining Agreement, by the NHL Department of Player Safety for roughing Rangers forward Pavel Buchnevich.
Panarin, Buchnevich and Capitals defenseman Brenden Dillon also received roughing minors as part of the incident.
Panarin did not return to the game.
"A defenseless player in Panarin, in my opinion, with no helmet on, a superstar in our league," Rangers center Ryan Strome said. "It's unfortunate our best player is out for the rest of the year. It's an unfortunate incident that has nothing to do with the play or the game of hockey."
Panarin scored 40 points (12 goals, 28 assists) in 28 games after returning to the lineup March 13, tied with Edmonton Oilers center Connor McDavid (14 goals, 26 assists in 21 games) for second in the NHL behind Colorado Avalanche forward Nathan MacKinnon (42 points; 14 goals, 28 assists in 25 games) following a leave of absence for personal reasons that kept him out for nine games. He was on the ice for 51 of the Rangers' 102 goals in the past 28 games.
He leads the Rangers and is 11th in the NHL with 58 points (17 goals, 41 assists) in 42 games. Panarin's 1.38 points per game is fourth behind McDavid (1.82), Oilers forward Leon Draisaitl (1.46) and MacKinnon (1.41).
"He just had another phenomenal year," Rangers coach David Quinn said. "The guy just continues to produce offense. He's a threat every time he's on the ice and he makes everybody around him better."
Panarin finished tied for third in the NHL with 95 points (32 goals, 63 assists) in 69 games last season. He was third in the voting for the Hart Trophy, given annually to the player judged most valuable to his team as voted on by members of the Professional Hockey Writers' Association. He has scored 153 points (49 goals, 104 points) in 111 games since signing a seven-year, $81.5 million contract with the Rangers on July 1, 2019.
Trouba has missed the past seven games; Kreider has missed three in a row; Lindgren has missed the past two.
