SEATTLE — One way or another, the Phillies’ starting rotation depth was going to be challenged this season.

The next two days may represent the toughest test yet.

With neither Zack Wheeler nor Zach Eflin cleared to return from COVID-19 protocols, left-hander Bailey Falter joined the team here Tuesday and will be added to the roster to start Wednesday’s matinee series finale against the Seattle Mariners.

But after Falter opened the season in a long-relief role, his arm isn’t stretched out to throw more than 60 to 65 pitches, according to manager Joe Girardi. Falter threw only 40 in his last start for triple-A Lehigh Valley last Friday night.

Oh, and the Phillies don’t have a starter for Thursday night’s series opener at Dodger Stadium, either.

Girardi said “there’s a chance” that Wheeler or Eflin, or both, will be allowed to return by then. But it’s too early say for sure. Vaccinated players must be cleared by MLB to be reinstated. Unvaccinated players aren’t cleared until they submit two negative PCR tests.

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Wheeler and Eflin were placed on the COVID-19 list last Sunday. A player can receive that designation for various reasons, including testing positive, exhibiting symptoms, or being identified as a close contact of someone who has the virus.

“We’ve got to make sure that everyone passes,” said Girardi, who isn’t at liberty to go into details about the status of Wheeler and Eflin but said earlier in the week that he was hopeful one or both may return during the four-game series in Los Angeles.

Falter and fellow left-hander Cristopher Sánchez are effectively the Phillies’ sixth and seventh starters. They have combined for a total of three major-league starts and 38 appearances — and a 5.45 ERA. Hans Crouse, also on the 40-man roster, has an 11.05 ERA in three triple-A starts this season.

Sánchez, who started the second game of a doubleheader on Sunday, could be an option to pitch Thursday on short rest. Another possibility: long reliever Nick Nelson, who hasn’t pitched since his 46-pitch appearance in relief of Sánchez.

Girardi said he wasn’t certain if the Phillies would be able to piece together Thursday’s game by using relievers, especially since the bullpen will have to cover several innings behind Falter. The Phillies also will have to make a move to get Falter on the roster.

It begs the question of whether the Phillies whiffed in not adding another depth starter in the offseason. They addressed the bullpen with Brad Hand and Jeurys Familia, beefed up the lineup with Kyle Schwarber and Nick Castellanos, and even brought back Odúbel Herrera to play center field.

But when it came to starting pitching, the Phillies stood pat.

They may regret that decision over the next few days.

Stott sits

Rookie shortstop Bryson Stott began Tuesday night on the bench with the Phillies facing a left-handed starter (Seattle’s Robbie Ray). Stott was 1-for-11 with four strikeouts since being recalled from triple A last weekend.

Stott was on the Phillies’ opening-day roster and went 4-for-30 before getting sent to the minors. He swung the bat well at Lehigh Valley, going 12-for-36 with two doubles, one triple, and two homers.

“I think his approach has been his approach, and it was really good for the time that he went down and had success down in triple A, and we expect him to have success here,” Girardi said. “I don’t make too much of 10 at-bats. I really don’t. I think think it’s facing big-league pitching, and it’s a big difference.”

Johan Camargo started in Stott’s place. Stott is expected to start Wednesday, according to Girardi. It’s unclear how much Stott will play in Los Angeles, where the Phillies are scheduled to face lefties Tyler Anderson, Clayton Kershaw, and Julio Urias.

Extra bases

Bryce Harper, relegated to being a designated hitter because of a strained right forearm, will be checked again next week, at which time the Phillies will determine if he can resume a throwing program. ... Entering Tuesday night, Phillies pitchers were eight strikeouts shy of 100,000 in franchise history, according to the Elias Sports Bureau. Only the Cubs, Dodgers, and Giants franchises have more. ... The Phillies acquired right-hander Corey Oswalt from the San Francisco Giants and sent him to triple A. Oswalt, 28, has a 5.89 ERA in 26 major-league games (14 starts), all for the New York Mets. ... The Phillies will face Mariners right-hander Logan Gilbert (4-0, 1.36 ERA) at 3:40 p.m. Wednesday.