Phillies place Spencer Turnbull to on 15-day IL. What's next for baseball's best rotation?

PHILADELPHIA (CBS) — MLB's best starting rotation is about to get its depth further tested.

The Philadelphia Phillies on Thursday placed Spencer Turnbull on the 15-day injured list with a right lat strain and recalled reliever Yunior Marte from Triple A Lehigh Valley. Phillies manager Rob Thomson said Turnbull will miss at least six weeks.

Turnbull left the Phillies' 6-2 win Wednesday over the Detroit Tigers after 36 pitches with right shoulder soreness. He said he felt it on his second-to-last pitch.

"I threw a curveball and I felt something grab my back in my triceps/shoulder area," Turnbull said. "It just got a little tight, but I didn't want to do anything to make it worse."

The 31-year-old was making his first start at Comerica Park as an opposing player. Turnbull spent five seasons with Detroit and was drafted in the second round of the 2014 MLB draft. He threw a no-hitter with the Tigers in 2021, but he underwent Tommy John surgery shortly after. He missed 2022 and appeared in only seven games last season because of neck and toe injuries.

Detroit optioned Turnbull to Triple A on Aug. 23 last season. He later filed a grievance, saying he was injured at the time. He was granted a full year of service time for 2023, reversing two minor-league options. The Tigers didn't tender him a contract last November.

"I don't know what it is about this place, but I can't seem to stay healthy here," Turnbull said. "I don't know if it is cursed or what."

Turnbull returned to the rotation this week after the Phillies placed Taijuan Walker on the 15-day IL on Sunday with inflammation on his right finger. Philadelphia's rotation is now down two starters.

In his first season with Philadelphia , Turnbull has a 2.65 ERA in 17 games and seven starts — he has a 1.78 ERA as a starter.

What happens now with the Phillies' starting rotation?

Philadelphia enters Thursday's series opener against the Miami Marlins at Citizens Bank Park with baseball's best pitching staff. The Phils' rotation leads MLB with a 2.96 ERA — the New York Yankees are next-best at 3.32 ERA.

But with Walker injured — and ineffective before his second IL stint of the season — and Turnbull now also hurt, the rotation depth will be tested. Thomson said Thursday that rookie Michael Mercado will slide into the rotation.

The Phillies acquired Mercado from the Tampa Bay Rays in November. The hard-throwing righty impressed in spring training and was used as a starter with the IronPigs before his call-up.

Mercado made his MLB debut in the Phils' 8-1 win over Detroit on Monday, striking out one batter in a clean eighth inning.

After Mercado, though, the Phillies' starting pitching depth in the minors is thin. Prospect Mick Abel 's struggles this season have taken him out of the equation, so veteran Kolby Allard or Tyler Phillips may be next up on the depth chart.