Feldman left Tuesday's start after 2⅔ innings with discomfort in his throwing shoulder. An MRI on Wednesday revealed no damage, and he received a cortisone injection to calm the inflammation.
The Astros hope he will be OK after sitting out one start.
Feldman led the American League with a 1.33 ERA in August. He left in the third inning of Tuesday night's 7-5 loss to the Seattle Mariners after walking five and giving up three hits and three runs.
Feldman walked two straight batters before grimacing after a pitch to Mark Trumbo that resulted in a fly out for the second out of the third inning. Trainers visited with him briefly on the mound before he left the game and was replaced by Vincent Velasquez.
"It felt worse and worse," he said after the game. "It felt tight at the beginning of the game, but [then] it started feeling to where it was actually starting to hurt. You got to try to know the difference between tightness and putting yourself and the team in a bad position. Once I started hurting, I don't want to go out there and tear my shoulder."
He returned from the disabled list July 18 after missing almost two months following arthroscopic surgery on his right knee.
Overall, Feldman has a 3.90 ERA and 5-5 record in 2015.
Information from The Associated Press was used in this report.