Cristoforo, who joined Sevilla from Penarol in August last year, sustained a blow to his left knee as Sevilla eased to a 4-1 La Liga win over Real Valladolid on Sunday.
And scans on Monday revealed that the 20-year-old will require surgery after rupturing his anterior cruciate ligament.
Unai Emery's men are also going to have to cope without Russian winger Denis Cheryshev, who has suffered a fractured metatarsal.
A statement on Sevilla's official website read: "Following scans on Monday, Sebastian Cristoforo has been diagnosed with a rupture of the anterior cruciate ligament of the left knee.
"The estimated period he will be out is six months after he undergoes his operation, the date of which has yet to be determined.
"In the case of Cheryshev, a fracture of the fifth metatarsal of the right foot has been confirmed. He will undergo surgery in Madrid on Thursday."
