Will Spencer Turnbull stay in the pitching rotation when Taijuan Walker returns?

Taijuan Walker, who is on the injured list with right shoulder soreness, will start his rehab assignment on Thursday night in Clearwater, Fla. He’ll throw 60-65 pitches and build up in 15-pitch increments. Manager Rob Thomson expects Walker to have four rehab outings before he rejoins the big league club.

This would be a more pressing issue if Spencer Turnbull didn’t have an 0.00 ERA over his last two starts. Turnbull was signed with the expectation of being a reliever but was rapidly built up after Walker went on the injured list in spring training. He has been nearly flawless in first two starts of the season, allowing just one walk and five hits with 13 strikeouts.

He’s added a sweeper to his repertoire, which has been a useful weapon for him — to the tune of a 33.3 whiff percentage — and has seen his strikeout rate double from 2023 to 2024. It’s a small sample but an intriguing one.

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Turnbull has a lengthy injury history but said he feels as good as he has in years. The Phillies will monitor his workload (he pitched only 31 innings in 2023 and missed the 2022 season after undergoing Tommy John surgery), but it’s not unrealistic to think he could stick around in the rotation even after Walker returns.

“Sure [there’s a path for him],” Thomson said Thursday. “I mean, if he keeps putting up zeroes. That’s tough to take him out of the rotation. But we’ll see.”

It’s unclear what that would look like right now, but Thomson responded to a few possibilities. He said piggybacking and going into a six-man rotation — later in the season — would be options. They tried a six-man rotation last summer, but there were some drawbacks. Zack Wheeler pitches significantly better on four or five days rest than he does with six days of rest.

The numbers reflect that. His ERA on 4 days of rest was 2.09, and 4.35 over five days of rest. His ERA over six-plus days was 4.94. Hitters hit .258/.314/.430 against him on six days rest, as opposed to .247/.281/.403 over five days and .189/.250/.277 over four days.

If they do go with a six-man rotation, it won’t be anytime soon.

“At times, like we did last year,” Thomson said. “I would think once we get deeper into the season, and when you don’t have an off day, when you have a long stretch like you do right now. We can’t afford to have a six man right now. But, yeah, that’s always [an option].”

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Walker has seen stretches of dominance — he points to his six-week span from May 21 to June 29 last season as an example — but has struggled to find consistency. His velocity has yet to return to where it normally is (Walker was around 90 mph throughout the spring and in his live batting practice sessions so far), but it’s unclear how much of that has to do with his injury. His velocity fluctuated last year, as well. He posted a 4.38 ERA through 31 starts with an 18.8% strikeout rate and a 9.7% walk rate.

We should have more clarity on where Walker is at as he begins his rehab assignment, and gets closer to returning to the big league club. In the meantime, Turnbull has four more opportunities to force the Phillies to make a tough decision.

Reliever Orion Kerkering (right forearm strain) will pitch one inning in Clearwater on Thursday night. He and Walker will return to Philadelphia on Friday, and the Phillies will map out a plan for their return.

Regardless of what they decide, Kerkering will not pitch Saturday. The Phillies have been using him one day on, one day off and would like to give him two days of rest before he returns to the big-league club.