The Pittsburgh Penguins might have to open their NHL season against the Washington Capitals without captain Sidney Crosby.
Crosby was a late scratch from Saturday's final exhibition game against the Columbus Blue Jackets because he "was not feeling well".
The Penguins said the skipper missed practice on Monday to undergo concussion testing, for which the results came back positive.
Coach Mike Sullivan told reporters Crosby was injured in practice Friday but would not get into specifics.
Pittsburgh begin their Stanley Cup title defence against Washington on Thursday.
Crosby's concussion history provides cause for concern. He missed the last half of the 2010-11 season and the first 20 games of the following campaign after suffering a concussion in early January 2011.
The issue cropped up again in December 2011 and he sat out more than three months before returning in mid-March.