The Green Hornet star dislocated a bone in his pelvis after falling off a horse while training for the spaghetti Western.
The incident has forced him to pull out of a promotional appearance at the New York Film Festival, according to WENN.
"Christoph Waltz was injured while training with his horse in preparation for his role," a spokesperson said. "He is currently being treated for a dislocated pelvic bone."
Waltz won an Oscar for his role as Col. Hans Landa in Tarantino's last project Inglourious Basterds.
He will star alongside the likes of Jamie Foxx, Leonardo DiCaprio and Samuel L Jackson in Django Unchained, which is due for release on Christmas Day 2012.
Watch the trailer for Inglourious Basterds below: