Manager Paul Molitor made the announcement Wednesday, according to Chip Scoggins of the Minneapolis Star Tribune. Castro was placed on the 10-day disabled list with a meniscus tear in his right knee earlier this month.
Originally his injury was thought to be minor. But the 30-year-old traveled to Colorado for a second opinion and it was determined he'd need surgery.
The Twins inked Castro to a three-year contract worth $24.5 million in November 2016. He was hitting .143/.257/.238 before the injury, but is highly regarded for his pitch framing.