Stuttgart and Germany striker Cacau will be out of action for at least three months after tearing both his medial and cruciate knee ligaments in training.
The Brazilian-born 31-year-old suffered the damage to his left knee on Wednesday after colliding with defender Antonio Ruediger.
Cacau, who has scored once in 10 games for the Bundesliga side this season, is wearing a special splint on the area in an attempt to avoid an operation, which would keep him out for longer.
"This is obviously very bitter for us and I'm really sorry for Cacau," said Stuttgart's director of sport Fredi Bobic.
"We will support him with everything we can do.
"We're thinking positively and we are hoping that he won't need an operation."