Bundesliga club Stuttgart says striker Cacau will be out of action for at least three months after injuring his left knee in training.
Stuttgart says the Brazil-born Germany striker ruptured his cruciate ligament in training on Wednesday.
Club doctors hope Cacau can avoid surgery.
"This is really bitter for us and I feel very sorry for him. We will do all we can to support him and hope that he doesn't have to undergo an operation," Stuttgart sports director Fredi Bobic said.
The club has won only one of seven games this season and is 15th in the 18-team top division.
Hoffenheim claimed a vital 3-1 win against second-tier Kaiserslautern in the first leg of the Bundesliga play-off.