Perez was struck in the mask in Saturday night's 12-inning, 4-3 win over the Mets in at Citi Field, latest in a series of blows he's taken in the chin and jaw recently.
"It's just a freak deal," Yost said. "That mask actually has more padding than any other mask you can get. It makes it more shock-absorbent. He just got hit in the wrong place."
Perez sustained a cut chin on July 24 against the Orioles.
"Nick [Kenney, head trainer] said it hit so hard it split the skin. It wasn't the mask," Yost said. "It's like a boxer getting punched in the jaw and that's where he got it, right in the jaw."
Two days later, Perez took another shot at Chicago.
"I'm hoping it's going to be seven days, but Corey Koskie played for me in Milwaukee and dove for a ball, it didn't look like much and it ended his career," Yost said. "So, I've learned to treat these things very, very carefully."
Right fielder David Lough, who left Sunday's game at New York with a tight right quadriceps, was out of Monday night's lineup against the Twins and will probably sit on Tuesday night as well.
"He's not playing today and there's a lefty [Justin Albers] going tomorrow so I'm probably not going to play him because I've got [Justin] Maxwell now," Yost said.
Second baseman Chris Getz, on the 15-day disabled list with a left knee sprain, was scheduled to join Triple-A Omaha at Salt Lake City and play Monday and Tuesday. He's eligible to come off the DL next Monday.
Dick Kaegel is a reporter for MLB.com. Kathleen Gier is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.