The Brewers placed Zastryzny on the 15-day injured list Wednesday with a left trapezius strain, Adam McCalvy of MLB.com reports.
Zastryzny was just activated Sunday after missing the first two months of the season with shoulder and intercostal strains, but he's heading back to the IL without having made an appearance. It's unclear whether this is a setback of one of the lefty's initial injuries or a new issue, but either way, the Brewers will likely take things slowly with Zastryzny.