The Pirates placed Howard on the 10-day injured list Tuesday with a right oblique strain, Alex Stumpf of DKPittsburghSports.com reports.
The lefty appeared in five games after being activated from the IL on June 29, posting a 16.20 ERA in 3.1 innings while walking four batters and hitting two. It's currently unclear whether Howard will be activated soon after he's eligible July 20. The Pirates have yet to announce a corresponding move.