Yelich described his condition as a "slight" bulging disk.
"I should be all right after a few days," Yelich said. "Just stay on it and take care of it, now that I know what it is."
Yelich had been dealing with back discomfort since April 12. He played on April 13 at Atlanta, but sat out the next two games, and he felt he made progress.
Yelich played in the four-game series at the Mets last weekend, but was not effective, going 2-for-18 with eight strikeouts.
The MRI was able to identify the problem.
"I didn't really know what it was, what was causing it," Yelich said. "I kind of had an idea. I got an MRI yesterday, and that kind of confirmed what everybody was thinking. Now I just have to stay on top of it, do some strength exercises and it should be fine."
Although Yelich is hopeful the 15 days will be all the rest he needs, the Marlins are being mindful not to rush anything.
They don't want the issue to linger or reoccur. So if he needs more time, he won't be rushed.
Yelich -- .200/.265/.222 with one double this year -- missed time last season with a low back strain. The left-handed-hitting outfielder was on the DL from June 16-19, 2014.
When he returned, he was healthy for the rest of the season.
With Yelich on the DL, Ichiro Suzuki has been playing regularly in left field.
Joe Frisaro is a reporter for MLB.com. He writes a blog, called The Fish Pond. Follow him on Twitter @JoeFrisaro. This story was not subject to the approval of Major League Baseball or its clubs.