The move leaves Cincinnati with more uncertainty over its fifth starter's spot.
The 31-year-old Fogg got hit hard again on Saturday, when he botched a chance to get back into the rotation. He gave up seven hits and six runs in 3 1/3 innings of an 8-7 win over Atlanta.
After the game, Fogg complained about back spasms.
"We need some pitching help bad," manager Dusty Baker said. "We can't wait."
Fogg started the season in the rotation, but was demoted to long relief after three poor starts. He went 15 days between appearances out of the bullpen.
The Reds optioned right-hander Matt Belisle to Triple-A on Tuesday to turn him into a reliever. Fogg was given a chance to start against the Braves, and could have regained his spot in the rotation with a strong showing.
Majewski failed to make the team in spring training. He went 2-1 with a 3.76 ERA in 22 relief appearances with three saves in the minors. The Reds aren't sure who will take fill the open spot in the rotation.