PHILADELPHIA -- The Giants were already down a catcher after placing Patrick Bailey on the seven-day concussion list prior to Saturday night’s game at Citizens Bank Park. Hours later, they lost another one.

The club saw its catching depth further thinned after Tom Murphy suffered a left knee injury in a 14-3 blowout loss to the Phillies on a cold, soggy night in Philadelphia.

With Bailey sidelined after taking a foul ball off his face mask on Friday night, the Giants tapped Murphy to start behind the plate on Saturday, but he said he felt a pop in his knee after going down to try to block a wild pitch amid slick field conditions in the second inning. Murphy immediately took himself out of the game and returned to the visitors’ dugout, slamming his mask on the bat rack in a show of frustration.

The 33-year-old veteran is expected to undergo an MRI exam on Sunday, but he described his concern level as “pretty high.”

“It doesn’t seem great,” manager Bob Melvin said. “It feels like it’s significant.”

Blake Sabol, who was called up from Triple-A Sacramento to replace Bailey, took over behind the plate, but it’s unclear who the next man up will be now that Murphy is likely heading for the injured list. The Giants have Jakson Reetz at Sacramento and No. 23 prospect Adrián Sugastey and Andy Thomas at Double-A Richmond, but none are on the 40-man roster.

“We’re definitely getting tested there,” Melvin said.

The Giants might also need a fresh arm on Sunday, as their bullpen was forced to cover 7 1/3 innings after rookie Keaton Winn recorded only two outs in a disastrous outing against the Phillies. Winn, who was battling a sinus headache in addition to the rain, had trouble gripping his trademark splitter and gave up five runs on four singles, two walks and a hit-by-pitch in the shortest start of his young career.

Earlier in the afternoon, San Francisco believed its biggest loss of the day would be Bailey, who was shelved after being struck on the head by a pitch fouled off by Alec Bohm in the first inning of the Giants’ 4-3 loss to the Phillies on Friday night.

Bailey wasn’t placed in concussion protocol immediately after the game, but he continued to experience blurry vision when he woke up on Saturday morning, prompting San Francisco to err on the side of caution with its second-year backstop. Bailey, 24, was also placed on the concussion list last September, when he missed six games following a home-plate collision with then-Cubs infielder Jeimer Candelario.

“As far as these things go, hopefully it’s mild,” Melvin said. “Based on the fact that he’s had these before, it was an easy decision to make. He woke up with kind of the same conditions as last night. Hopefully, it’s just a seven-day thing. I think it was last year. But you can’t be too careful about this.”

Losing Bailey is a significant hit for the Giants, as he’s emerged as one of the top defensive catchers in the league and has also been one of the club’s most productive bats to start the year, hitting .278 with an .800 OPS and three homers through 25 games.

Without Bailey and Murphy, the Giants will likely lean on Sabol to handle regular catching duties.

Sabol said he hopped on a red-eye flight through Phoenix shortly after Bailey was pulled and ended up landing in Philadelphia around 5 a.m. ET on Saturday morning. The 26-year-old spent the entire 2023 campaign with the Giants after sticking as a Rule 5 Draft pick, but he opened this year at Triple-A Sacramento, where he was batting .243 with a .702 OPS and one home run over 21 games.

Sabol went 2-for-3 after subbing in for Murphy, though he also committed a catcher's interference error in the sixth inning that helped the Phillies score four runs (one earned) off No. 28 prospect Randy Rodríguez, who tossed 2 1/3 innings in his Major League debut.

Sabol said it was difficult to return to the Minors after being left off San Francisco’s Opening Day roster this year, though he tried to take the demotion in stride and use the time to continue to refine his catching skills, particularly his blocking and throwing.

“It was definitely different,” Sabol said. “For me, that was the first time in my baseball career kind of taking a step back and getting demoted, which was a good learning opportunity for me. That was definitely a little bit of time to feel sorry for myself, in a way. Once I got down [to Triple-A] and I was in the locker room with my teammates and stuff, it was like, ‘OK, this is a good team down here.’ So I didn’t feel like it was a slap in the face by any means. It was just be where your feet are and try to win games."