Ahead of Mason Black’s major-league debut Monday afternoon, the Giants needed to create space for the 24-year-old right-hander on the 40-man roster.

Choosing to designate Daulton Jefferies for assignment, rather than transfer Tom Murphy to the 60-day injured list, indicated that the backup catcher’s knee sprain suffered Friday night was not as severe as initially believed.

Indeed, Murphy is expected to miss only 4-6 weeks, manager Bob Melvin said before first pitch Monday. MRIs revealed a Grade 1-2 sprain in his left knee but nothing that would require surgical intervention.

“Anything non-surgical is good news,” Melvin said. “Especially the way he felt and was speaking to. Anytime you lose a guy for a significant period, it’s not great.”

At least until Patrick Bailey (concussion) is eligible to be activated Friday, the Giants were left with Jakson Reetz and Blake Sabol as their catching duo. Against right-hander Zack Wheeler on Monday, it was Reetz behind the plate.

Sabol received the start Sunday and graded out well framing strikes, Melvin said.

“We look at those kind of things, and it was actually a good day for him,” Melvin said. “It’ll be a mix between the two. It could be more righties for Blake and more lefties for Jakson. We’ll have Reetz today, but we’ll see where it goes. It’s probably more of a lefty-righty type thing.”

The positive news regarding Murphy made Jefferies the obvious 40-man casualty, but it wasn’t an easy conversation for Melvin, who managed the 28-year-old right-hander in Oakland and witnessed him make an unlikely comeback from multiple Tommy John surgeries and a thoracic outlet procedure.

“I’ve got a history with him,” Melvin said. “He’s gone through, shoot, what feels like four months of moves during the first month of the season. This is one where we’ll see what happens. If he gets picked up, he goes to the big leagues. Great, I’m happy for him. If not, he has a decision to make. Hopefully we can get him back in this organization and see where we go from there. But a lot of hard work to get back to where he was and he should be proud of himself.”

In two appearances for San Francisco, Jefferies had allowed 13 runs (nine earned) in 4⅔ innings, a 17.36 ERA, while opposing hitters batted .487 against him.

If all goes well Monday, Black could fill the vacant spot in the starting rotation until Blake Snell is ready to return.

Snell (adductor) emerged healthy from a three-inning bullpen session Sunday and will progress Tuesday to facing live hitters. Snell is scheduled to throw three simulated innings, and Melvin has said previous they hope to have the two-time Cy Young winner back by the end of the month.