Ludvig was put on long-term injured reserve Wednesday, rather than the regular IR, with an upper-body injury, per Matt Vensel of the Pittsburgh Post-Gazette.
Ludvig consequently isn't eligible to return until Jan. 27 versus Montreal at the earliest, assuming this move is retroactive to Sunday, which is when he was last in the lineup. The 23-year-old defenseman has an assist in 19 contests this season. Pierre-Olivier Joseph is likely to play regularly while Ludvig is unavailable.