The 25-year-old Lamet was hurt during his final start of spring training on March 25 and began the season on the disabled list.
Manager Andy Green said Friday that Lamet was the closest of the organization's young pitchers to earn a spot at the top of the rotation this season.
"It's tough for all of us," Green said. "He was going to be the guy we looked to to anchor our staff this year and we were hopeful right after the injury that he'd be able to avoid surgery. ... Disappointing, to say the least, and tough for him. The hope and expectation is sometime next year he'll be back on the mound pitching for us. He's a guy we still have a ton of faith in, a ton of belief in. It's a tough loss."
Lamet made his big league debut last year, going 7-8 with a 4.57 ERA in 21 starts, with 139 strikeouts and 54 walks.
"It's not something that's good to go through, but sooner or later in this career, in this game, I think it's something you might have to deal with," Lamet said through an interpreter. "You never expect it, you never want it to happen but you know it's a reality."
Lamet said he felt tightness in his elbow after throwing a slider on March 25.
He took a week off and then started a throwing program. Once he got up to 90 feet, he had another MRI and decided to have the surgery.
"Despite everything, I definitely feel fortunate to be where I am, to have been able to show in spring training that the work in the offseason paid off, to have earned what I earned and to know I was in position to have success," he said.
Lamet's injury opened the way for lefty Joey Lucchesi to be promoted from the minors. While nothing is imminent, Green says lefty Eric Lauer could be the next of San Diego's hotshot pitching prospects to be called up.