ST. LOUIS -- Considering the alternative, there is some encouraging news for Marlins right-hander Pablo López.

Tests confirmed that Lopez is dealing with a right shoulder strain. The 23-year-old was examined in Miami on Wednesday by team medical director Dr. Lee Kaplan and underwent an MRI. There is no structural damage, and his condition is considered mild.

The Marlins placed Lopez on the 10-day injured list on Wednesday. On Thursday, their No. 18 prospect, Zac Gallen, made his MLB debut in place of Lopez against the Cardinals at Busch Stadium.

“It seems like it was generally pretty good news,” Marlins manager Don Mattingly said of Lopez’s status. “So, we’re giving him a little bit of rest and then building him back up. In general, you didn’t go and see something, where you go, ‘Oh, no.’ So, you feel pretty good about that.”

To create 40-man roster space for Gallen, the Marlins designated first baseman/outfielder Peter O’Brien for assignment. Reliever Jeff Brigham was optioned to Triple-A New Orleans.

Even with the optimistic medical report on Lopez, the Marlins are tasked with managing the innings for a rotation that has become depleted the past few weeks.

Lopez is the third Marlins starter to land on the IL this month, joining left-hander Caleb Smith (left hip inflammation) and right-hander Jose Urena (herniated disc). Urena is on the 60-day IL, while Smith and Lopez are on the 10-day.

Smith is tentatively scheduled to begin a rehab assignment on Monday, and if that goes well, he could be back in the rotation by the end of the month.

The two holdovers from the Opening Day rotation are Trevor Richards and Sandy Alcantara. Richards, 26, has the most MLB experience of the current five, with 40 big league starts under his belt. Alcantara is next with 20.

Jordan Yamamato has made two, Elieser Hernandez has two this year and eight in his career and Gallen on Thursday took the mound for the first time at the big league level.

“That’s what we’ll be doing, is really just keeping an eye on them and where they were last year, and where we need to keep their innings,” Mattingly said.

Richards, who threw 5 2/3 innings in a no-decision on Wednesday, has 84 innings this year and 210 1/3 in his two-year career.

Alcantara is at 82 innings in 2019, and in 2018 he had 127 at Triple-A and 34 with Miami.

Smith has 66 innings in 12 starts this season, after logging 77 1/3 in 2018. So, when he gets back, the left-hander will be closely watched.

Yamamoto had 68 2/3 innings a year ago, splitting time at Class A Jupiter and Double-A Jacksonville. He’s already at 79 1/3 innings between New Orleans and the Marlins (14).

Urena is the most seasoned starter, with 126 total appearances and 93 starts. He has thrown 74 2/3 innings.

“We didn’t really come into the year with any innings limits on guys, knowing that we’re going to probably have to get them out of there for a turn or two, and things like that,” Mattingly said. “It will be the same, continuing to manage them.

“We don’t really have any restrictions, where you say, ‘This guy can’t throw past 110 innings.’ Or anything like that.”

Worth noting
• The Marlins announced two additional signings from the 2019 Draft class: catcher Thomas Rowan (Round 20, No. 591) from UC Santa Barbara, and right-hander Brock Love (Round 34, No. 1011) out of the University of Alabama. Miami has now signed 24 of its 41 picks.

• Miami's Competitive Balance A selection, outfielder Kameron Misner (35th overall) from the University of Missouri, is not yet close to signing. The deal likely will get done. The deadline to sign picks is July 12 at 5 p.m. ET.