SAN FRANCISCO -- The Giants’ playoff hopes took a significant hit after starting catcher Patrick Bailey landed on the 10-day injured list with a right oblique strain on Tuesday.

Bailey was expected to start Monday night’s series opener against the White Sox, but he was a late scratch after tweaking his side while taking early swings on the field prior to the game. He described the soreness as “very, very minor” and said it was more of a precautionary scratch, but the Giants had him undergo an MRI exam on Tuesday, which revealed the oblique strain and ultimately forced him on the IL for the third time this season.

Manager Bob Melvin said the Giants wanted to tread carefully with Bailey, who could be back as soon as he’s eligible to return on Aug. 29 at Milwaukee.

“I’m pretty optimistic that on that 10th day, he should be ready to go,” Melvin said following the Giants’ 4-1 win over the White Sox. “I think based on what I’m hearing and how he’s feeling, we were a little bit cautious with this one. If you go out there even a game too early and you re-injure that thing, it could be a long time. We were pretty cautious here and I’m hoping it’s the last day in Milwaukee that he could come back.”

The Giants will lean on veteran Curt Casali and Jakson Reetz -- who was recalled from Triple-A Sacramento on Tuesday -- to fill in behind the plate in the interim, though it will be hard to replace Bailey’s Gold Glove-caliber defense.

Bailey has slumped badly in the second half, hitting only .115 with a .292 OPS over his last 27 games, but he remains one of the most impactful defenders in the league, leading the Majors in both Fielding Run Value (19) and Catching Framing Runs (14) this year.

“It is hard,” Melvin said. “He’s one of those guys that’s tough to replace even when he’s not swinging the bat well. At times this year, he’s hit in the middle of the order for us, too. But Curt’s doing a good job right now. He’s on a little bit of a roll. He did a great job with Robbie today. He’s caught [Logan Webb] really well, too. We’ll see where we go with it.”

Tuesday marked the first time the 35-year-old Casali had started on back-to-back days for the Giants since May 18-19, when Bailey was out with a concussion. He’s expected to make it three in a row and catch Webb in Wednesday’s series finale at Oracle Park as well.

“Obviously it sucks that [Bailey] had to go on [the IL], but it’s kind of par for the course for catchers in this game,” Casali said. “It’s hard to avoid that list at some point, especially when you’re catching as much as he has been. But I think we got pretty decent news on his scan, so I’m happy for that. Personally, I’m just going to have to grind. This is a good opportunity for me to get behind the plate and play a little bit more and hopefully show what I can do and help the ballclub win.”

The Giants signed Tom Murphy to be Bailey’s primary backup this season, but the 33-year-old veteran appeared in only 13 games before landing on the IL with a left knee sprain in May. Murphy has started a hitting and throwing progression, but it remains to be seen if he’ll be able to return before the end of the season.