Lowrie's injury is to the peroneal nerve, which is a branch of the sciatic nerve and supplies movement and sensation to the lower leg. He will be on crutches and wear a protective brace for at least a week before beginning rehab exercises.
"From what the doctor told me, I'll just have to wear the brace for a week or two and let the ligament tighten back up and then start the rehab process," Lowrie said.
Lowrie was hitting .253 with a club-best 14 homers and 36 RBIs through 80 games and losing him is a big blow to an Astros team that had batted just .201 in the previous 15 games before Tuesday.
Marwin Gonzalez, a Rule 5 pick last December, will get most of the playing time at shortstop for now, but general manager Jeff Luhnow hasn't ruled out going outside the organization for shortstop help.
"He's done a good job and we're certainly thankful we have him, but we need to consider other options, whether it's bringing up somebody else from Triple-A or looking outside the organization," Luhnow said. "At this point it could go faster, but four to six [weeks] is what we're expecting."
Lowrie has spent time on the disabled list in each of the last four seasons, including this year, when he injured his thumb in Spring Training. He hurt his shoulder last year in a collision with Red Sox teammate Carl Crawford and missed time in 2010 with mononucleosis.
"I've never approached it as being frustrating," he said. "There's nothing I could have done any differently. I was playing the game and trying to get an out. I just have to get it better and get back out there."
Meanwhile, catcher Jason Castro, who was also played on the disabled list on Sunday (retroactive to July 8), had his ailing right knee examined Tuesday in Houston. Astros manager Brad Mills said Castro's knee is still swollen and shows some meniscus damage, but Luhnow remains hopeful Castro can return with a week.
"We're still hopeful it's going to be a short-term situation and he can come back when he's eligible and shortly after," Luhnow said. "We'll know more in the next couple of days."
Castro, who missed all of last season after undergoing ACL surgery on his right knee, was hitting .254 with two homers and 20 RBIs in 20 games this year but had begun to experience some soreness in the knee.
"He's going to have more fluid drained [Wednesday] and hopefully we'll know more in three or four days," Luhnow said.