Mariners send top prospect Tyler O'Neill to Cardinals for Marco Gonzales

SEATTLE -- The Seattle Mariners paid a hefty price to add a pitcher who might not be ready to help them in the playoff hunt this season.

The Mariners acquired young left-hander Marco Gonzales from the St. Louis Cardinals on Friday in exchange for top outfield prospect Tyler O'Neill, the second move to add pitching depth in as many days by Seattle. The Mariners acquired veteran reliever David Phelps from Miami on Thursday.

While Seattle will have Gonzales under club control for a number of seasons, he may not be the impact arm to help the Mariners in this year's chase for a wild-card spot in the American League. Gonzales has pitched once in the majors this season as he continues to recover from Tommy John surgery that sidelined him for the entire 2016 season.

Seattle is expected to have Gonzales begin at Triple-A Tacoma.

"Marco is a quality athlete with high character and a strong pitching pedigree who we feel fits our roster well in both the near and long term," Seattle general manager Jerry Dipoto said in a statement. "We find his current performance, preparedness and proximity to the major leagues to be very appealing traits in a pitcher, particularly a young lefty who is now under club control through the 2023 season."

Gonzales, 25, has deep ties to the Pacific Northwest -- he was a collegiate star at Gonzaga -- and makes his offseason home in Seattle. He showed flashes of promise early in his career with the Cardinals, but injuries have derailed most of the past two seasons. He missed parts of the 2015 season due to a pectoral injury and then needed elbow replacement surgery that kept him out all of 2016.

Gonzales was 6-4 with a 2.90 ERA in 11 starts at Triple-A Memphis this season, and since June 18 was 5-1. His one start in the majors didn't go well. He gave up five earned runs in 3⅓ innings in a loss to Milwaukee.

Gonzales thanked St. Louis in a tweet Friday afternoon.

Seattle paid a significant price for Gonzales. O'Neill was considered one of the top prospects in Seattle's farm system and had been on a tear lately at Triple-A Tacoma, with five home runs in his last five games. The 22-year-old O'Neill had 19 home runs in 93 games at Triple-A, and two years ago he hit 32 home runs in the Single-A California League.

"You've got to separate outfielders from something sort of like defensive profiles to offensive profiles. The one thing that we talk a lot about is finding those bats. This is a player that has a lot of offensive upside. At 22, he has accomplished a lot already at Triple-A. So, for us, it just adds to our offensive depth," Cardinals president of baseball operations John Mozeliak said.

O'Neill played for Team Canada in the World Baseball Classic and was rated among the top five prospects in Seattle's farm system by a number of organizations.

"We definitely feel like our strength is starting pitching in our minor leagues, not that we aren't proud of our outfield guys. But we do like his offensive profile," Mozeliak said.

The Cardinals also activated outfielder Randal Grichuk and reliever Zach Duke from the disabled list and recalled catching prospect Carson Kelly from Triple-A Memphis.

Catcher Eric Fryer was designated for assignment by the Cardinals before Friday's game against the Chicago Cubs. Right-hander Sam Tuivailala and outfielder Magneuris Sierra were optioned to the minors after Thursday's 3-2 loss to the New York Mets.

Grichuk had been sidelined by a lower back injury. He made a rehab appearance with Double-A Springfield on Wednesday and went 1-for-4 with a three-run homer.

Duke, 34, is coming back from Tommy John surgery in October. He went 2-1 with a 2.36 ERA in 81 games last season for St. Louis and the Chicago White Sox.

The Associated Press contributed to this report.