That was one of a series of roster moves announced by the Royals prior to Sunday's finale.
Catcher Brett Hayes was called up from Triple-A Omaha to take Perez's place on the 25-man roster.
Starting pitcher Wade Davis was placed on the family emergency list and pitcher Will Smith was recalled from Omaha to join the staff. Davis left the Royals during the first inning of Saturday's game because of a medical emergency involving his brother.
The emergency list is for an absence of three to seven days. Davis is next scheduled to start on Wednesday against Minnesota.
Hayes will join backup catcher George Kottaras in filling in for Perez, who is hitting .278 with four home runs, 19 doubles and 43 RBIs. Smith will work out of a bullpen that has been worked hard in two extra-inning games with the Mets.
Perez took a shot in the mask from a foul ball in the 12th and last inning of the Royals' 4-3 win on Saturday. He finished the game but had a headache and was taken to a hospital for tests.
"I saw him get hit and I didn't think anything of it, but his jaws were sore because the mask jarred him back or whatever," manager Ned Yost said.
"Always after the game, he'll come over and give me a hug, right? But he didn't yesterday. So I said, 'What's wrong with you?' And he said, 'Uh-uh-uh,' and then he gave me a hug. He goes, 'I've got a headache, my head's hurting.' So I knew something was wrong there. We took him right into the training room, the doctors came, they took him to the hospital and they cat-scanned him. The headache had subsided, he was clear and he answered questions. But they still deemed it a low-grade concussion, and they don't play with that stuff."
Perez has also taken other hard blows to the mask this season and recently suffered a cut chin when struck by a ball.
He was released from the hospital on Sunday morning and rejoined the Royals at Citi Field.
"He can't do anything until all his symptoms resolve themselves," Yost said. "He's not disoriented but just has a headache."
Perez was also very tired after a somewhat sleepless night at the hospital.
"I told him as soon as the game starts he could sprawl out on my [office] couch and sleep," Yost said.
After Sunday's 6-2 victory over the Mets, Perez said, "I've still got a headache, and my chin is sore."
But he had felt well enough to grab something to eat and was very hungry.
"I ate at McDonald's and it tasted like filet mignon," he said.
Kottaras started Saturday's game to give Perez a scheduled day off, but Perez entered the game in the eighth inning. Kottaras is batting just .172 but actually has more homers than Perez (five), and with 17 walks, he has an on-base percentage of .354.
Yost said he'd "juggle" the two catchers, but Kottaras was in the lineup Sunday.
Hayes, who lost the backup job to Kottaras in Spring Training, had a .231 average, 11 homers and 34 RBIs in 68 games for Omaha. Earlier this year, when Perez missed eight games because of his grandmother's death in Venezuela, his roster spot was taken by catcher Adam Moore. But Moore recently underwent surgery for a groin tear and is out for the season.
The Royals claimed Hayes off waivers from the Miami Marlins last November. He'd been with the Marlins for four years as a backup catcher, batting .217 in 143 games.
Smith has a 6-3 record, three saves and a 3.03 ERA this year for Omaha. He started 10 games but then was switched to the bullpen, where he worked 16 games as a reliever. He last pitched on Friday.
"I definitely need the arm today," Yost said.
This is Smith's fourth stint with Kansas City this season, including twice as the 26th man on the roster for doubleheaders. He's pitched six times for the Royals, with a 1-1 record and 3.86 ERA. In 16 1/3 innings, he's notched 15 strikeouts against only one walk.