Letang (lower body) was placed on injured reserve Tuesday, per the NHL media site.
Pittsburgh activated Marcus Pettersson (lower body) from injured reserve in a corresponding move. Letang won't be eligible to return until at least Jan. 5 against Carolina following his placement on the IR list. He has amassed seven goals, 16 points, 84 shots on net, 43 blocked shots and 56 hits in 34 appearances this season.