Yelich, the Marlins' No. 2 ranked prospect by Baseball America, will start in left with Marisnick in center.
To make room for the two outfielders, the Marlins optioned infielder Derek Dietrich and outfielder Marcell Ozuna to Double A Jacksonville.
"I want to make this really clear, that the offensive woes of this team I don't want attributed to them," said Larry Beinfest, president of baseball operations, in making the announcement. "That's not why this is happening. Those kids did an incredible job. We rushed them here to the big leagues out of need. They had almost no Double A experience, and they did a great job for us."
But it was clear in watching their at bats in Milwaukee that Dietrich and Ozuna were struggling badly.
"We just thought it warranted a time to go down to the minor leagues and work on some offensive things on both their parts," Beinfest said. "We asked a lot of them, putting them in the middle of the lineup. They're part of our future, and part of our future is coming as well."
Yelich and Marisnick started Monday for Jacksonville but were each taken out after reaching base in the third inning.
The Marlins have had high hopes for Yelich after since they drafted him in the first round in 2010. They acquired Marisnick among a package of players in the blockbuster deal with Toronto last November.
"This is a good time to bring them and have them bet the experience," Beinfest said. "As a general rule, we don't like sitting young players, and they're not coming here to sit."
The Marlins will have to make room for Yelich and Marisnick on the 40-man roster, most likely with players already on the disabled list, Beinfest said.
• Angel Sanchez, one of the three minor-league pitchers the Marlins received from the Dodgers in the Ricky Nolasco trade, started and worked six innings on Monday in a combined no-hitter for Single A Jupiter. Sanchez, a 23-year-old right-hander, struck out three while walking two.
Colby Suggs and James Nygren pitched the final three innings to complete the no-hitter.
Sanchez has made three starts for Jupiter since the July 6 trade with Los Angeles, going 2-0 with a 1.69 ERA.
• While the Marlins finally ended their team scoring drought, Justin Ruggiano remained in his hitting slump. Ruggiano went 0 for 4 Monday and has now been hitless in his past 31 at bats. The team record is 33 at bats without a hit, held by Mike Jacobs.