Matheson (lower body) is expected to miss Wednesday's game in Washington, per Marco D'Amico of BPM Sports.
Matheson also missed Tuesday's 4-3 shootout win over Buffalo due to the injury. He has an assist, six PIM, two hits and 10 blocks in five appearances with the Canadiens this season. Matheson is considered day-to-day, so he still might return to the lineup Saturday versus the Sabres. The 32-year-old should regain his top-four spot once he's healthy.