Pressly takes the place of catcher Garrett Stubbs on the 25-man roster. The Astros optioned Stubbs to Triple-A Round Rock following Wednesday's victory over the Rockies.
"It's good to get [Pressly] back," Astros manager A.J. Hinch said Friday. "It's nice to have our bullpen intact."
Pressly suffered a right knee contusion after being struck by a comebacker off the bat of the Angels' Andrelton Simmons on July 18. The right-hander pitched twice more as he tried to work through discomfort -- including a rough outing against the Cardinals in which he allowed three earned runs without recording an out -- before going on the IL on July 27.
The 30-year-old Pressly worked one scoreless inning Tuesday in his rehab assignment for Double-A Corpus Christi. He struck out two of the three batters he faced.
In the midst of a career year, Pressly is on pace to set career highs in earned run average (2.03), WHIP (.857) and strikeout-to-walk ratio (6.88).
Hinch expressed zero hesitation about using Pressly in his traditional setup role right off the bat.
"He's still one of the best relievers in baseball," Hinch said of Pressly. "He'll be right back in his normal role."
Right-hander Brad Peacock is inching closer to a return as he works back from right shoulder discomfort.
Hinch said the plan for Peacock, who has been on the injured list since June 28, is to throw back-to-back days Saturday and Sunday for Round Rock. Houston plans to re-evaluate whether he needs more time with his rehab after those appearances.
"We're going to bring him to Chicago and evaluate him," Hinch said. "Once we see him, we'll see if he needs more outings or if he's good to go."