Reliever T.J. Beam was promoted from Triple-A Indianapolis to fill the roster spot.
Dumatrait, a left-hander, was 3-4 with a 4.66 ERA but had been Pittsburgh's most consistent starter since joining the rotation May 2. But the 26-year-old's two previous starts were his worst of the season. He allowed 14 runs in 10 innings in two losses.
In the short term, the Pirates plan to move up each of their other starters a turn in the rotation because of a scheduled off day Monday.
The 27-year-old Beam has a 2.02 ERA in 26 games with 39 strikeouts in 40 innings in Triple-A, holding opponents to a .201 average. The right-hander had allowed just three earned runs in 22 1/3 innings over his past 16 appearances.
Beam's only prior major league experience came with the Yankees in 2006, going 2-0 with an 8.50 ERA in 20 games covering 18 innings. He was signed by the Pirates as a minor league free agent in December.
To clear space on the 40-man roster for Beam, the Pirates transferred injured outfielder Chris Duffy from the 15-day disabled list to the 60-day list.