PEORIA, Ariz. -- With Opening Day still eight days away, the Mariners suffered a big blow Wednesday, as they announced that right-handed reliever David Phelps needs Tommy John surgery and will miss the upcoming season.

Phelps tore his ulnar collateral ligament on the final pitch of his last outing Saturday against the Angels. Typical recovery from Tommy John surgery is 12-15 months.

"There's no way to sugarcoat it," general manager Jerry Dipoto said. "He's a big piece of what we're doing here, and it's a big loss for us. He will feel it, his teammates will feel it and we'll feel it. The good thing is we do feel we have some depth to work back from, but it won't be an easy spot to fill. There's a reason we went and got him, a reason we were excited for his return. He'll be missed."

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Phelps was acquired last July in a trade with the Marlins and pitched just 10 games before being sidelined by elbow problems that eventually led to surgery to remove a bone spur.

The Mariners were counting on the 31-year-old Phelps to be a major part of their bullpen this season, as he was expected to split time with free-agent acquisition Juan Nicasio and Nick Vincent in a three-way setup situation for closer Edwin Diaz .

Phelps is earning $5.5 million this year in his final season of arbitration eligibility. He will be a free agent after the season, but he will remain with the Mariners in Seattle to do his rehab.

Phelps pitched in five games this spring, and the Mariners were excited about how he looked early in camp.

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"He was really prepared and came into the spring off the bone chip and looked great," Dipoto said. "Physically, the stuff was right where it needed to be, and the last thing we were waiting for was the precision. Oddly enough, the last outing, when the precision joined the stuff, is when he wound up hurting himself."

Phelps' injury will likely create more late-inning opportunities for Dan Altavilla , who has had an excellent spring, and open up a roster spot potentially for Chasen Bradford , Ryan Cook or Shawn Armstrong , who was recently sent to Minor League camp. The Mariners also just acquired right-hander Erik Goeddel from the Rangers on a waiver claim. But having previously lost Tony Zych to shoulder issues and with Nick Rumbelow sidelined indefinitely by a nerve issue in his neck, the expected depth has definitely taken a hit.

"The combination of trio of events with Tony Zych, Nick Rumbelow and now Phelps, that's not exactly how we planned the spring to go with that group," Dipoto said. "You know you'll run into an occasional injury and lose players along the way, but to have three in that time span is tough to deal with. Fortunately, we're at the time of year when players are a little more accessible."

With Phelps' departure, the Mariners will have three openings on their 40-man roster, and Dipoto indicated he'd likely acquire more pitching in the coming days as other teams make roster cuts or have players out of Minor League options.

Phelps is a six-year Major League veteran who began his career as a starter with the Yankees before being converted to a relief role by the Marlins in 2015.

The Mariners gave up four Minor Leaguers -- outfielder Brayan Hernandez and right-handed pitchers Pablo Lopez , Brandon Miller and Lukas Schiraldi -- last July 20 to acquire Phelps. He had a 3.12 ERA in 8 2/3 innings over 10 outings, but he spent 15 days on the disabled list in August with elbow problems and was then shut down for the remainder of the season on Sept. 1.