"He's had a sore knee for the better part of a couple weeks," Hinch said before Monday's series opener vs. the D-backs. "I saw him favoring it a little bit yesterday, and he had a little bit of difficulty going up and down steps. So we talked after the game, and it had gotten to the point where it was affecting virtually every aspect of his game. He could continue to catch, but his offense has obviously taken a step back. His comfort and footwork with catching, his mobility ... it just wasn't good. So I think he needed to go see a doctor, he needed to get his tests. We need to find out if there's a solution for him to feel a little bit better."
McCann is batting .232 with 13 home runs in 75 games in his debut season with the Astros. The 33-year-old seven-time All-Star is in his 13th season and has split the catching duties with Evan Gattis, who is currently on the 10-day DL with a concussion.
Juan Centeno got the start at catcher Monday for the Astros. Along with McCann being placed on the DL, the Astros selected the contract of Max Stassi from Triple-A Fresno.
Stassi, whom the A's selected in the fourth round of the 2009 MLB Draft out of Yuba City High School in California, has played in a handful of games for Houston each year since he was acquired by the Astros in 2013. He was hitting .266 with 12 homers in 73 games at Fresno this season.
"I think he has had a nice year," Hinch said. "He's watched Centeno come up a couple different times and he's continued to play pretty well and make a case for himself. ... He makes for a good partner for Centeno back behind the plate. I have right-handed, left-handed options. Both of them are familiar with our staff, which makes me comfortable."
Hinch said he won't necessarily decide who starts at catcher each day based on left-handed or right-handed matchups. With the Astros down to their third- and fourth-string catchers, Hinch praised the team's organizational depth.
"Usually you have three [catchers]," Hinch said. "And that third guy has that experience, he's the emergency guy. To have a fourth guy that has Major League experience, especially inside our own organization, is pretty rare. It's important, because it's not easy to come up and learn the staff."
Jarrid Denney is a reporter for MLB.com and covered the Astros on Monday.