Guerin was injured in overtime during the Sharks' 3-2 loss to the Red Wings on Wednesday night. Defenseman Christian Ehrhoff's shot was deflected straight at Guerin, who dropped to the ice and left a pool of blood before skating to the dressing room.
The Sharks said Thursday that Guerin is doubtful for Game 5 in the best-of-seven series Saturday in Detroit.
Guerin has been a disappointment in the playoffs for the Sharks, who gave up forward Ville Nieminen, prospect Jay Barriball and a draft choice in a trade-deadline deal with St. Louis to acquire the veteran goal-scorer specifically for his experience and playoff poise.
But Guerin has no goals in nine playoff games, managing just two assists and a minus-3 rating. Coach Ron Wilson has used him on various lines in an effort to spark the four-time all-star, to no avail.
Game 6 in the second-round series is Monday night in San Jose.