The Mariners have confirmed that rookie right-hander Ljay Newsome will start Tuesday in what would have been Taijuan Walker’s next turn before he was traded to Toronto on Thursday. Now the question is whether Seattle will actually get to play that game Tuesday against the A’s at T-Mobile Park.

The A’s postponed their game on Sunday against the Astros after a member of their organization tested positive for COVID-19 and the team will remain quarantined in Houston on Sunday night instead of flying to Seattle for a Monday off-day as initially planned.

The Mariners still have a game Monday in Anaheim to close out a four-game series with the Angels before returning home for that Tuesday encounter, but they will now await word from MLB on the status of the A’s before that scheduled three-game set opens in Seattle.

If things go as scheduled, Newsome will make his second Major League start, having filled in for Walker on short notice Thursday in San Diego. The 23-year-old threw four innings while allowing just three hits and one run in that contest.

With Newsome now in the rotation, the Mariners have four starters age 24 or under, with Justin Dunn, Justice Sheffield and Nick Margevicius all 24, along with veterans Marco Gonzales, 28, and Yusei Kikuchi, 29. Newsome, Dunn and Sheffield are all rookies.

Newsome pitched primarily at Class A Advanced Modesto last season before closing out the year with nine starts at Double-A Arkansas, but he’s pitched well in his first two Major League outings, including three innings of one-run ball against the Dodgers in relief in his MLB debut.

“He’s earned it,” Mariners manager Scott Servais said. “He did a really nice job against a good Padres lineup the other day. We’ll fire him out there. Nothing really phases Ljay. Like I told him when he was starting the other day, I said, ‘Are you OK with that?’ And he goes, ‘I suppose.’ He’s just, ‘Tell me when I’m pitching, and I’m good to go.’ It’ll be a good challenge for him.” 

How many starts Newsome gets remains to be seen, as the Mariners are sticking with their six-man rotation for now, but they have four off-days in the final three weeks of September and could go with five starters through that stretch while maintaining essentially the same workload.

Short takes

• Reliever Seth Frankoff was added to the Mariners’ 28-man roster from their alternate training site prior to Sunday’s game, with fellow right-hander Zac Grotz optioned back to the alternate training site. Frankoff, 32, was on the traveling taxi squad for the current road trip, but he now joins the Major League roster for the first time since signing with Seattle on a Minor League deal on Aug. 11.

Frankoff was in Padres camp this spring and spent the 2018-19 seasons pitching in Korea, where he went 27-11 with a 3.68 ERA in 50 starts. Servais said Frankoff is stretched out and could work in a long relief role if needed.

Grotz pitched 1 1/3 innings in Saturday’s 16-3 loss, allowing four runs on three hits, four walks and a hit batter.

Reliever Matt Magill was transferred to the 45-day injured list to open a spot on the 40-man roster for Frankoff. 

• The Mariners also added catcher Joe Hudson off the taxi squad prior to Sunday’s game, with outfielder Braden Bishop optioned to the alternate training site. Hudson has hit .125 (2-for-16) in eight games with Seattle this year and provides some additional depth behind the plate.

With Evan White just returning from a shoulder issue after sitting out the past three games, starting catcher Austin Nola also is a backup option at first base and Hudson provides additional depth behind the plate if needed.