The Pirates placed Howard on the 10-day injured list Sunday due to right knee tendinitis.
The injury likely played a part in Howard's worst outing of the season Friday, when he was lit up for six runs on four hits and two walks while retiring just two Cleveland batters. The disastrous showing moved Howard's season ERA from a tidy 2.45 all the way up to 4.44. Pittsburgh recalled lefty Austin Davis from Triple-A Indianapolis to fill Howard's spot in the bullpen.