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Mariners to start prospect Bryan Woo Saturday while Marco Gonzales undergoes tests on throwing arm

Seattle Mariners pitcher Marco Gonzales throws against the Cleveland Guardians on April 8 at Progressive Field in Cleveland. Gonzales will undergo season-ending surgery.   (Getty Images)
Ryan Divish Seattle Times

ARLINGTON, Texas — The depth of the Mariners’ young pitching talent in their farm system will be tested again as another rotation regular appears headed for the injured list.

Veteran left-hander Marco Gonzales didn’t make the trip to Texas with the team and is in Seattle undergoing tests on his left forearm.

“He felt a little discomfort after his last start,” manager Scott Servais said before Friday’s game. “He threw his bullpen the other day, and it didn’t feel great, so he wanted to get it checked out.”

Right-hander Bryan Woo, the Mariners’ No. 6 prospect in the organization per MLB Pipeline, arrived in Texas on Friday to take Gonzales’ spot on the roster and in the starting rotation. Servais confirmed that Woo will make his MLB debut vs. the Rangers.

The roster move won’t be made official until Saturday morning. The Mariners also will have to open a spot on the 40-man roster for Woo. They could transfer Robbie Ray, who had season-ending elbow surgery, to the 60-day injured list.

“He’s got good stuff,” Servais said of Woo. “He’s got a really good fastball. He’s young. He’s learning.”

Servais watched Woo pitch during spring training and came away impressed.

“He’s got really good composure,” Servais said. “That’s what stood out for me in spring training. Again, big-league spring training is different than the regular season. Any guy that makes his debut is always going to be a little anxious and hyped up and ready to go, but I’m looking forward to seeing him pitch.”

Woo, 23, has made nine starts for Class AA Arkansas this season, posting a 3-2 record with a 2.05 ERA. In 44 innings he’s struck out 59 with 12 walks. He was named the Mariners’ minor-league pitcher of the month for May and April.

Seattle selected Woo in the sixth round of the 2021 draft out of Cal Poly even though he’d had Tommy John surgery three months before the draft. He returned to the mound in June 2022 and made 16 starts, posting a 1-4 record with a 4.11 ERA. But he was outstanding in the Arizona Fall League, going 2-0 with an 0.84 ERA in five starts.

Because of his limited innings pitched in 2022, the Mariners were going to be cautious with Woo’s workload even before he was promoted to the big leagues.

Save for two bad outings, Gonzales has been solid in the No. 5 spot this season. He has a 4-1 record and 5.22 ERA, and the Mariners are 7-3 in his 10 starts. In his most recent outing vs. the Pirates he pitched 5 2/3 innings, allowing one run on three hits with three walks and four strikeouts.

He’s been durable since being acquired in 2017, going on the injured list just twice — once late in the 2018 season due to a lower-back strain. In 2021 he was sidelined because of a forearm strain April 29 and returned June 1.