Pressly, 33, has been sidelined this week with neck spasms.
"His neck is not any better. About the same or worse," manager Dusty Baker told reporters ahead of the team's home game against the Minnesota Twins.
The right-hander has 25 saves this season for the AL-best Astros. Righty Seth Martinez was recalled from Triple A.
Baker also said right fielder Kyle Tucker is day-to-day with a foot injury that plagued him at the beginning of the season. He has a career-best 16-game hitting streak.
And center fielder Chas McCormick, who left Wednesday's win against the Twins after injuring his right pinky while sliding back on a pickoff attempt, will likely miss two days with a dislocated finger.
"We've got quite a few guys who are kind of wounded, but not really hurt hurt," Baker said. "We're trying to prevent them from getting hurt."