Pena (hamstring) will begin a rehab assignment Tuesday, likely at Double-A Corpus Christi, Brian McTaggart of MLB.com reports.
Pena will go through a full workout Monday first, and as long as he gets through that without any hiccups, he'll play in his first game in more than a month Tuesday. The shortstop could be back on the Astros' active roster before the end of this week.