Tommy John surgery.

The Washington Nationals rookie sensation is done for the season — and maybe next season as well — after the team announced Friday that he has a torn ligament in his right elbow. He will travel Saturday to the West Coast for a second opinion, but the 22-year-old right-hander has accepted the fact that he will need the ligament replacement operation that requires 12 to 18 months of rehabilitation.

“It’s a new challenge,” Strasburg said. “I want to be the best at everything, and right now I want to be the best at rehabbing and getting back out here.”

It’s a blow to Strasburg, of course, and to a baseball world that has spent the summer gasping in awe at his 100 mph fastball, bending curves and wicked batter-freezing changeups, but the biggest punch to the gut is to a Nationals franchise that had made the young phenom the centerpiece in their plans to climb out of perpetual last-place irrelevancy.

“There’s no words that I can put in place here that would indicate we could possibly replace Stephen,” manager Jim Riggleman said. “But we have to do it a different way, different names, different staff members who will go out there and fulfill the rotation until Stephen comes back.”

Strasburg grimaced, grabbed and shook his wrist after throwing a 1-1 changeup to Domonic Brown in Philadelphia on Saturday. It turned out to be his last pitch of the year. The Nationals initially called the injury a strained flexor tendon in the forearm, but an MRI taken Sunday raised enough questions for the Nationals to order a more extensive MRI in which dye was injected into the prized right arm.

Strasburg had the exam on Thursday and was informed of the diagnosis later that night, but the Nationals chose not to announce the news until because it would have upstaged the introductory news conference for 2010 No. 1 draft pick Bryce Harper.

Strasburg could hardly believe the bad news, especially because his arm has felt fine all week, certainly good enough to keep pitching.

“I didn’t take a matter of minutes” to sink in, he said. “I took definitely a few hours. I’ve got great support all around me, and they reminded me of everything I should be thankful for, and they put everything in perspective for me. Bottom line, this is a game. I’m very blessed to play this game for a living. It’s a minor setback, but in the grand scheme of things it’s just a blip on the radar screen.”

Strasburg is an intense, competitive man. He wants the ball. He was disappointed when he had to start the season in the minors and wasn’t exactly thrilled with the restrictions the Nationals have placed on him. Now he faces something he’s never experienced in his baseball life: surgery on his arm, and the realistic prospect of not pitching again until 2012.

“It’s a new challenge,” he said. “It’s going to be a learning experience. I feel like I’m going to be able to grow a lot as an individual and as a baseball player.”

Strasburg said that on Friday he plans to write down on a piece of paper everything he’s thinking and look at it again a year from now. He’s said he’s doing it he knows his mind might “get a little jumbled” as he goes through rehab and that he wants to remember everything he needs to focus on.

And as far as trying to figure out why this has happened to him? He’s done with that question.

“If I keep looking for an explanation, it’s just going to eat at me, and I’ve got to let it go,” he said. “I’ve just got to move on, and that’s what I’m doing. Everything happens for a reason, and this is obviously going to be a test for me.”

The No. 1 overall pick in the 2009 draft, Strasburg signed a record $15.1 million contract a year ago. He struck out 14 batters in an amazing major league debut in June and was quickly drawing huge crowds everywhere. He went 5-3 with a 2.91 ERA and 92 strikeouts in 68 innings with the Nationals, who kept him on strict pitch counts and had planned to shut him down once he reached about 105 innings.

But he has had medical setbacks despite the team’s best efforts to be as cautious as possible. He was placed on the disabled list a month ago because of inflammation in the back of his right shoulder. He was making his third start since returning from the DL when he had to leave the game against Philadelphia.

“The player was developed and cared for in the correct way, and things like this happen,” Rizzo said. “Pitchers break down, pitchers get hurt and we certainly are not second-guessing ourselves. … Frustrated? Yes. But second-guessing ourselves? No.”

Rizzo said doctors believe Strasburg tore the ligament on a particular pitch — perhaps the changeup to Brown — as opposed to a gradual deterioration over a long period of time. When Strasburg grimaced in game at Philadelphia, he told the team he had felt something similar at San Diego State and had continued to pitch through it. Doctors have decided that what happened in college was unrelated to the ligament tear.

The injury is the last thing the woebegone Nationals needed. The franchise is on pace for its fifth last-place finish in six years since relocating from Montreal. Attendance has been disappointing at Nationals Park since it opened in 2008, but Strasburg generated rare sellouts in his first few home starts.

Coincidentally, Thursday’s game marked the return of Jordan Zimmermann, another promising Washington pitching prospect who had Tommy John surgery a year ago. Strasburg and Zimmermann are supposed to form two-fifths of a rotation that will lead the team to respectability.

“It’s still going to happen,” Riggleman said of the Strasburg-Zimmermann combo. “It’s just going to be another year before it happens.”

Strasburg has already received advice from Zimmermann and can draw inspiration from the dozens of major leaguers who have successfully returned from the surgery that was first performed by Dr. Frank Jobe on Los Angeles Dodgers pitcher Tommy John in 1974.

“That’s the modern miracle of what doctors can do to put people back together,” Twins manager Ron Gardenhire said recently after a game that featured Tommy John returnees Francisco Liriano and Tim Hudson. “We all know the arm takes a beating. Goodness gracious, we saw two guys who were both throwing the ball 90-plus mph with sliders and stuff. That’s because some doctors did some really good jobs.”

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AP Baseball Writer Jon Krawczynski in Minneapolis contributed to this report.