The Toronto Maple Leafs revealed on Wednesday to-4 weeks with a separated shoulder.
Lupul apparently suffered the injury during the second period of a 5-4 home loss to the Boston Bruins on Tuesday. The 28-year-old is on his way to a career year, racking up 25 goals and 67 points in 66 games.
In that same game, forward Colby Armstrong was felled by a broken nose and is listed as day-to-day. Armstrong has had bad luck with injuries this year, limited to one goal and one assist in just 19 appearances.
Toronto recalled forward Carter Ashton -- son of former NHLer Brent Ashton -- from its AHL affiliate.