Marshall, who has been on the 15-day disabled list since April 10 (retroactive to April 8) because of tendinitis in his left shoulder, will make another appearance on Wednesday when the Bats host Gwinnett.
"I will be in the mix with the relievers tomorrow. Instead of starting a game, I will come in in relief like I usually would do," Marshall said.
When Marshall started for Louisville at Indianapolis on Monday, he threw 12 pitches -- including eight strikes -- in his lone inning.
"It felt like my starting pitcher days. I got to throw in the first inning," Marshall said. "It's been a while since I've done that. I treated it like a relief appearance. I was warming up at about 6:57 [p.m.] and while the other pitcher was throwing in the top of the inning, I pretty much went from the bullpen to the mound.
"Everything felt good. I took it like it was a real game. I threw all of my pitches -- curveballs, sliders and fastballs. Everything felt good coming out of my hand."
What happens after Wednesday remains unknown. Marshall became eligible for activation on Tuesday.
Mark Sheldon is a reporter for MLB.com. Read his blog, Mark My Word, and follow him on Twitter @m_sheldon This story was not subject to the approval of Major League Baseball or its clubs.