Seattle Kraken forward Jacob Melanson is out indefinitely after being diagnosed with an anterior mediastinum hematoma and vascular pseudoaneurysm, the team said.

Melanson sustained an upper-body injury during Seattle’s 6-1 season-opening win at Calgary on Oct. 1. The diagnosis was announced Saturday. Kraken coach Lane Lambert said Sunday that Melanson was recovering and that the team missed him in the lineup.

The Kraken said their medical staff would closely monitor the 23-year-old as he heals and assess a gradual progression toward returning to hockey. Melanson had five points in 36 games for Seattle last season.