Castro left Monday's game with a sprained right knee, and manager Bo Porter told general manager Jeff Luhnow to get him another catcher as soon as possible.
"I'm glad we were able to get someone for no other reason than the health issues that have been going on with our catchers," Porter said.
The Astros have two catchers on the seven-day concussion disabled list -- Corporan and Max Stassi. Corporan was injured on Aug. 19 when he took a foul ball of his facemask, and Stassi was hit in the head by a pitch two days later and hasn't played since.
Corporan will begin a Minor League rehab assignment on Wednesday for Double-A Corpus Christi, which is in the Texas League playoffs. He will be the designated hitter the first game and will catch the second game with hopes of rejoining the Astros on Monday in Seattle.
"This has been crazy, the catching situation this year," Corporan said. "I'm trying to get back and help my team."
Stassi has said in recent days he hasn't been able to pass his balance tests.
"Stassi has one more hurdle left, and until he clears that milestone we're in a holding pattern," Luhnow said.
Cody Clark, a 31-year-old who was called up on Aug. 23 after 11 years in the Minor Leagues, replaced Castro and went 0-for-3 on Monday, dropping him to 0-for-13 for the season. The Astros didn't call up a third catcher when rosters expanded because their Triple-A affiliate in Oklahoma City, like Corpus Christi, is going to the playoffs.
"Both of those teams have played so well this year, and we want to give them every opportunity we can to win the whole thing," Porter said.
Castro, a two-time American League Player of the Week, is having a career season, hitting .282 with 18 homers and 56 RBIs after going 2-for-2 with two RBIs on Monday. He suffered his injury running the bases in the first inning.
Castro underwent an MRI on Tuesday that showed no structural damage to his right knee, which is the same knee on which he underwent surgery to repair his anterior cruciate ligament in 2011.
"We're breathing a sigh of relief on that," Luhnow said. "It's a lot better than it could have been."
Pagnozzi , who finished up his season at Triple-A Gwinnett on Monday, has appeared in 33 Major League games in his career with St. Louis (2009-10), Colorado (2011) and Pittsburgh (2011) and is a career .310 (22-for-71) hitter with one home run and 13 RBIs.
"I've got some history with him from my time in St. Louis, and so does [catching instructor Jeff] Murphy," Luhnow said. "He's an excellent defensive catcher with time in the big leagues with a couple of different clubs, and it's good fit for us for our catching depth."
Pagnozzi was beginning a drive to his home in Arizona from Gwinnett, Ga., and had just changed a bulb on the headlamp in his truck at a Walmart when he got the call he had to head to Houston.
"It's very exciting," he said. "Any time you can be a part of something like this, especially getting another month of playing baseball, I'm looking forward to it."
To make room for Pagnozzi on the 40-man roster, the Astros will transfer Edgar Gonzalez to the 60-day disabled list.