Giuseppe Rossi will be out of action for up to seven months after suffering a ruptured anterior cruciate ligament in his left knee during Celta Vigo's La Liga defeat at the hands of Eibar.
The 30-year-old attacker featured from the start in Sunday's 2-0 loss at Balaidos but was forced off 10 minutes before half-time.
He underwent a series of tests to determine the extent of the injury and Celta announced on Monday he will be require an operation and be sidelined for at least six months.
"Medical tests have revealed that Giuseppe Rossi has suffered a rupture of the anterior cruciate ligament of his left knee," a statement on the club's website reads.
"The player will need to undergo surgery and will be out of action for a minimum of six months.
"Celta wish Rossi a speedy recovery."
Rossi has been plagued by injury throughout his career, with the former Manchester United forward undergoing a number of operations on his right knee over the past few years.
The former Italy international joined Celta on a one-year loan deal from Fiorentina ahead of the 2016-17 campaign and has scored four times in 18 La Liga outings.