Blanco, 41, now becomes the primary backstop. The club signed veteran Humberto Quintero, 33, who was designated for assignment by the Phillies earlier this week. Quintero became a free agent Friday and arrived just in time for Friday night's game.
"We're going to lean on [Blanco] quite a bit from here on out," acting manager Robby Thompson said. "It's too bad because the reason why Hank is here was to mentor Mike and he's done a great job with him. He works with him all the time. He pulls for him every day. Mike is going to miss out on that for these 4-5 weeks, but I'm sure when he's out here, Henry will continue his tutelage with him."
Zunino, 22, has been the Mariners starting catcher since being called up from Triple-A Tacoma on June 12 and was hitting .242 with two home runs and 10 RBIs while helping solidify a position originally occupied this season by Jesus Montero.
Zunino initially thought a foul ball off his wrist had aggravated a previous sore spot, but it turned out he broke the hamate bone on a swing and miss in his second at-bat of Thursday's game. He'll undergo surgery early next week after an MRI exam Friday morning revealed the fracture.
The youngster said this is the first time he'll have to miss significant time in the middle of a season.
"It's frustrating, but it's just another thing you deal with as a player," he said. "It takes nothing away from the team. The team did a great job last night and hopefully they continue to do that. I'm just going to continue to get better as soon as I can to help them out again."
Trainer Rick Griffin said hamate injuries generally require about a six-week recovery, but noted that Ken Griffey Jr. played 23 days after he had surgery on his hamate in 1996.
Zunino was the third overall selection in the 2012 First-Year Player Draft and is regarded as one of the top young catching prospects in baseball. Over his last 11 games, he hit .324 and had the game-winning RBI in each of his last three starts for a Seattle club that has won 10 of its last 11 games.
Montero recently rejoined Tacoma after missing more than a month following surgery on a torn meniscus, but the Mariners have said he'll be limited to first base and designated hitter duties the remainder of the season.
Blanco, 41, has hit .156 in 11 games since being signed by the Mariners on June 14 after the team released Kelly Shoppach.
Jesus Sucre played eight games earlier this year, but remains on the disabled list with a bruised wrist. Thus the Mariners have had a revolving door with their catchers this season, but Thompson said it's part of the game.
"You move forward and continue on," he said. "There's no one that is going to feel sorry for us. That's the way it is. We'll move forward starting today."
Jason Jaramillo, a 30-year-old with some Major League experience, has been the starting catcher for Tacoma the past month, with Brandon Bantz working as his backup. But the Mariners went outside the organization to sign Quintero, an 11-year veteran who hit .250 with two home runs and nine RBIs in 24 games with the Phillies this season.
Quintero will need some time to adapt, but figures to split time quickly with Blanco. He is a career .235 batter who also has played with the Astros, Padres and Royals.
"Once we get him here, we'll sit down as a group and figure that out," Thompson said. "We'll probably split time and do the matchup thing and go from there. One thing about it, Henry does know the pitchers now and has caught most of them. So the next guy we bring in here, we'll pick our spots on how to break him in with our pitching staff."