Malenstyn notched an assist, two blocked shots and two PIM in Thursday's 6-1 win over the Rangers.
Malenstyn and the Sabres agreed to terms on a two-year, $2.7 million contract Tuesday, Elliotte Friedman of Sportsnet reports.
Malenstyn was traded to Buffalo from Washington for the Sabres' second-round pick, 43rd overall on Saturday.
Malenstyn (upper body) is expected to play Tuesday versus the Flyers, Bailey Johnson of The Washington Post reports.
Malenstyn (upper body) will be a game-time decision for Tuesday's regular-season finale versus the Flyers, Bailey Johnson of The Washington Post reports.
Malenstyn (illness) is expected to be available to play Sunday versus Arizona, per Bailey Johnson of The Washington Post.
Malenstyn (illness) is uncertain to play Sunday against the Coyotes, Bailey Johnson of The Washington Post reports.
Malenstyn tallied a goal and an assist in Monday's 6-3 win over the Senators.
Malenstyn (personal) will rejoin the Capitals on Saturday against St. Louis, Bailey Johnson of The Washington Post reports.
Malenstyn (personal) will not play Thursday against the Blues, Sammi Silber of The Hockey News reports.