The relief pitcher, who's been on the disabled list since June 11 with a sprained right elbow, rejoined the team following his Minor League rehab stint at Triple-A Oklahoma City, but he won't be activated until the second half of the season gets underway on Friday.
"If he goes through his throwing program today and feels good, we're anticipating activating him after the break," Astros manager Brad Mills said.
Lopez has been a key part of the Astros' bullpen the last few seasons, including this year in going 3-0 with a 2.51 ERA in 32 1/3 innings pitched. Fernando Rodriguez has taken Lopez's role in the bullpen, coming into games with runners on base.
Rodriguez has allowed only four of 25 inherited runners to score, despite a 6.25 ERA.
"Where Fernando has given up runs has been when he has to start an inning or after getting out of an inning and going out for the next inning," Mills said. "He's done such a good job getting out of innings and that's the role we used Lopey, and Lopey's done a good job.
"When we have two of those guys, that's fun for me, because that's another tool to use to help us later in games."