SEATTLE — One month after starting in center field for the Phillies on opening day, Matt Vierling is headed back to the minors.

The Phillies optioned Vierling to triple A before Wednesday’s game here against the Seattle Mariners. A roster move was necessary to make room for spot-starting left-hander Bailey Falter, although with Zack Wheeler expected to return Thursday from the COVID-19 list and start against the Los Angeles Dodgers, the Phillies could’ve sent down a pitcher.

Instead, they chose to demote Vierling, who was batting .170 with a .472 OPS in 54 plate appearances, and kept the bullpen stocked with 10 — count ‘em, 10! — relievers.

“I just felt like he was struggling a little bit and he needed to go get consistent at-bats,” manager Joe Girardi said. “We hadn’t seen a lot of lefties. His playing time was inconsistent. It just feels like he’s in between. We just felt like it was best for him, and what’s best for him will be what’s best for us.”

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Vierling, 25, won a share of the center field job in spring training and played every day at the outset of the season because Mickey Moniak broke the fifth metacarpal in his right hand on the eve of opening day.

But Vierling got off to an 0-for-15 start and gradually began to lose playing time once fellow center fielder Odúbel Herrera returned from the injured list two weeks ago. After starting 10 of the first 14 games, Vierling was in the lineup for only six of the last 16, mostly against left-handed pitching.

“You can start to press a little bit when you’re young,” Girardi said. “And it’s one thing if you know you’re playing every day. But when you’re not playing every day, you’ve got to sit on it and sit on it, and it probably becomes even more difficult. I think it’s getting some at-bats under his belt just to get him going, right?”

Still, the timing of the move is curious. Vierling is a right-handed hitter, and the Phillies are scheduled to face three lefty starters (Tyler Anderson, Clayton Kershaw, and Julio Urías) in a four-game series at Dodger Stadium that opens Thursday night.

But the Phillies also thought they needed pitching reinforcements for the series finale against the Mariners, with Falter stretched out for only about 60 pitches. Falter figures to be sent back to triple A to get Wheeler back on the roster.

The Phillies also were carrying six outfielders to compensate for Bryce Harper, who is unable to throw because of a strained flexor tendon in his right elbow. With switch-hitting Roman Quinn on the roster to back up Herrera, there was even less playing time for Vierling.

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”This is a kid that we really believe in,” Girardi said. “We really believe he’s going to make an impact for us. We’ve just got to get him on track.”

Wheeler ready; Eflin not yet

Wheeler and fellow starter Zach Eflin went on the COVID-19 list Sunday. Although Wheeler was due to meet the team in Los Angeles, Eflin’s status remained uncertain, according to Girardi.

A player can be put on the COVID-19 list for a variety of reasons, from actually testing positive to being deemed a close contact. The requirements for reinstatement vary, too. Vaccinated players must be cleared by MLB; unvaccinated players aren’t cleared until they submit two negative PCR tests.

Girardi isn’t able to discuss the circumstances that landed Wheeler or Eflin on the COVID-19 list. Asked what Wheeler, in particular, has been able to do over the last few days to stay active, the manager wasn’t specific.

“He kept his arm going,” Girardi said.

Wheeler hasn’t pitched since May 4 against the Texas Rangers. He has been on a roll lately, tossing 13⅔ scoreless innings over his last two starts.

With a day off Monday, the Phillies won’t necessarily need a fifth starter until a May 21 home game against the Dodgers, though they are hopeful of having Eflin back well before then.

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Extra bases

Backup catcher Garrett Stubbs started for only the fifth time in 31 games. ... Moniak has started taking swings in the batting cage at the Phillies’ complex in Clearwater, Fla. He’s likely still a few weeks from playing in games. ... Lefty reliever JoJo Romero faced hitters in live batting practice in Clearwater. Romero is two weeks removed from the one-year anniversary of having Tommy John elbow surgery. ... The Phillies will face Anderson (3-0, 2.78 ERA) in the opener against the Dodgers at 10:10 p.m. Thursday night. They thought they acquired Anderson before the trade deadline last year, but the Pittsburgh Pirates canceled the deal over concerns about the health of Phillies pitching prospect Cristian Hernandez.