Barnetta to undergo knee surgery
The Swiss international was injured during a friendly match against VfL Bochum on Tuesday.
"Obviously this is something you cannot change but it makes me angry," Barnetta said in a statement. "After the operation I will do whatever I can to get back as quickly as possible."
Leverkusen, who are fourth in the Bundesliga, 13 points off leaders Borussia Dortmund, welcomed Germany captain Michael Ballack back into action last week after a four-month injury layoff.