Franzen didn't play Saturday night against the Dallas Stars as a precaution because he's had recurring headaches dating to early in the previous series.
"We didn't know about it until this morning," captain Nicklas Lidstrom said after a 2-1 win gave the Red Wings a 2-0 lead in the series. "He hasn't really told anyone, maybe our doctors knew a little bit about it."
The Red Wings said Franzen will not play until he has more tests and an evaluation is completed. Franzen is scheduled for tests Monday in Detroit and will miss that night's Game 3 in Dallas.
Detroit general manager Ken Holland said Franzen has had headaches -- which the GM described as "nothing significant" -- since playing the Colorado Avalanche earlier this month, and they haven't subsided.
"We don't know if he's had a concussion," Holland said. "We're hoping to find out more after he goes through various tests this weekend and sees a specialist on Monday."
Franzen has scored an NHL-high 27 times since March 2, a 27-game roll that includes a league-high and franchise-record 12 goals in the postseason. He is the first player to score 12 playoff goals since Rod Brind'Amour for Carolina in 2006.
The player known as Mule matched a team playoff record with a goal in the series-opening win over Dallas, extending his scoring streak to five games. Gordie Howe pulled off the feat in 1949 and '64. Ted Lindsay scored in five consecutive games in 1952.