The 29-year-old grinder left Ottawa's 5-4 pre-season victory over the Montreal Canadiens on Thursday after twisting his ankle. With the injury, Ottawa loses a depth winger who was set to feature on the opening night roster.
Watson was acquired by the Senators from the Nashville Predators in October 2020 and produced 10 points in 34 games in the Nation's Capital last season. He spent his previous six seasons in Nashville after the Predators selected him 18th overall in 2010.
In other Senators roster news, goaltender Filip Gustavsson has been assigned to the AHL's Belleville Senators.