Eto'o was injured as he took a shot just two minutes after coming on as a substitute at the start of the second half of Wednesday's friendly with Inter Milan. Barcelona won 5-0.
Barcelona said Eto'o may have to undergo surgery and was expected to return to training in eight weeks.
The Cameroon striker's absence will at least solve coach Frank Rijkaard's selection headache for a while.
In Barcelona's opening game of the season against Racing Santander last Sunday, Rijkaard left Henry on the bench until the second half when he replaced Messi. The game ended scoreless.
Barcelona hosts Athletic Bilbao on Sunday.