Barcelona will be without striker Samuel Eto'o for up to five months after he underwent surgery for a serious knee injury on Thursday.
Eto'o scored 26 goals for Barcelona last season
The 25-year-old Cameroon international was carried off during Barca's 1-1 draw with Werder Bremen on Wednesday.
"The operation was to repair the meniscus of the knee, not take it out, which lengthens the recovery to eight weeks," said club doctor Ramon Cugat.
Eto'o will miss Barca's Champions League games with Chelsea in October.
He will also miss Barca's trip to rivals Real Madrid in La Liga on 22 October.
Eto'o, who was voted third in Fifa's World player of the year award for 2006, has been Africa's top player for each of the last three seasons.
He has hit 68 goals in 101 games for Barca and scored 26 times last season to finish the top scorer in Spain.
Barca lie second in Champions League Group A with four points from two games, behind Chelsea who have six points.
They are top of the Spanish League with 10 points from four games.