"I was told the ligament was torn and for the elbow to fully heal, an operation was the only option," the Japanese pitcher told a news conference.
"It was a shock, even though I was kind of prepared for the news. To be honest I feel a lot of anxiety right now.
"Many people told me the success rate for this kind of surgery is high. But it's the first time for me and it worries me. Only bad things seem to be entering my mind now."
The 30-year-old right-hander was placed on the 15-day disabled list last month when he was initially diagnosed with a sprained ulnar collateral ligament in the elbow.
Popularly known as Dice-K, Matsuzaka has gone 3-3 with a 5.30 ERA in eight appearances this season.
"I'm in the biggest pinch of my baseball career," said Matsuzaka when asked about his future with the Red Sox. "It's up to me to turn things around."
Matsuzaka helped Boston win the World Series in his first season of a six-year deal worth $52 million.
After a sparkling second campaign, when he registered an 18-3 record with a 2.90 ERA, he has struggled and has been booed by Boston fans at Fenway Park this season.
(Reporting by Alastair Himmer in Tokyo; Editing by Ian Ransom)