SAN FRANCISCO -- Giants manager Gabe Kapler has seen all the pitching the National League has to offer, and he puts the Brewers’ collection of arms near the top.

“I think there’s a couple of clubs that could make a case,” Kapler said Monday before the Brewers and Giants opened a four-game series at Oracle Park. “But the top of their rotation is as good as any in baseball. The back of their bullpen is as good as any in baseball. I think you know how I feel about [Brewers manager Craig] Counsell -- if you don’t, I have a ton of respect for the way ‘Couns’ and his staff manage that group and puts them in positions to succeed.

“In particular, I’m thinking about the back of the bullpen, but also through the middle of games. [The Brewers bullpen offers] some interesting looks. I’m not going to speak to anybody individually, but there are some interesting looks with some reverse splits that make it a little more challenging to match up against them. I can share this part of it: A few series back, we faced the A’s, and the A’s have some similar looks, where normally we would throw out some pinch-hitters that we’d feel really good about. Against their bullpen, it’s a little trickier.

“As good a staff as there is out there. … [Corbin] Burnes and [Brandon] Woodruff and [Freddy] Peralta, the three of them combined -- and this is not to take anything away from the other starters, but those are three powerful right-handed starters, for sure.”

Kapler is scheduled to see Burnes (2.30 ERA entering the series) and Woodruff (2.38 ERA) start the first two games this week, but he’ll miss Peralta (2.45 ERA).

On the 10-day injured list after experiencing shoulder inflammation earlier this month, Peralta threw a second, more extended bullpen session on Monday afternoon and is tentatively slated to rejoin the rotation on Friday at home against the Cardinals.

Kapler, of course, played for the Brewers in 2008, when the team was far better known for its collection of home-grown hitters than its pitching. But he cautioned against calling that a hit-first club.

“I think Ben Sheets and CC Sabathia might disagree with you,” Kapler said.

Outfield prospects Frelick, Perez promoted

Sal Frelick, the Brewers’ 2021 first-round Draft pick and No. 2 prospect by MLB Pipeline, has been promoted again to High-A Wisconsin while No. 4 prospect Hedbert Perez is moving up to Low-A Carolina, the organization announced Monday.

It’s the second promotion this season for Frelick, who was hitting .442/.500/.605 in his first 20 professional games between the Arizona Complex League and the Low-A level. And it’s the first move up for Perez, 18, who signed out of Venezuela during the 2019-20 international period. He slashed .333/.394/.575 in the ACL.

“We want to challenge guys in a good way, and this gives them an opportunity to see what he can do against better pitching,” Brewers GM Matt Arnold said of Frelick. “He’s shown that he is capable at those lower levels, and that is a great thing. We don’t want to rush guys too fast.”

And Perez?

“Tremendous. Great kid. Nothing but positive stuff,” Arnold said. “He’s done such a nice job hitting and we’ll see if he’s ready for the next level.”

The Brewers do tend to push players in their system. Take No. 3 prospect Brice Turang, who is a 21-year-old shortstop playing at Triple-A Nashville.

“There are a lot of factors in there besides the performance,” Arnold said. “What is the guy like off the field? Is he handling himself in the clubhouse? All the things you would want to see out of a future big leaguer. So there are a lot of ingredients that go into promoting guys, but we want to challenge these guys and move them up the level as responsibly as possible.”

Giants face pitching scramble

The Brewers opted not to change their lineup on Monday after the Giants made a last-minute switch to a lefty opener, José Álvarez, in what amounted to a bullpen game after San Francisco placed Johnny Cueto on the injured list along with Tuesday’s scheduled starter, Alex Wood.

Kapler said he was authorized to report that Wood had tested positive for COVID-19 and was substantially under the weather. Cueto, too, was dealing with what Kapler described as cold or flu-like symptoms. The Giants already were without second baseman Donovan Solano, who is on the COVID-related IL.

Kapler characterized the development as “a real concern” as the calendar flips to September.

“That doesn’t make us unique in any way,” Kapler said. “We know a lot of clubs have dealt with the virus and dealt with it successfully.”

That includes the Brewers, who lost nine players with the COVID-19 IL in a 12-day span in late July and early August, including eight who ultimately tested positive for the virus. Like the Giants are learning, there is some anxiety when each day brings the potential of new cases.

“I think we were just trying to be responsible through it,” Arnold said. “The guys who deserve a lot of credit are [Brewers medical director] Roger Caplinger and [head athletic trainer] Scott Barringer. To the extent we could limit it, those guys were great at keeping us on the field. There is no roadmap.”

Said Counsell: “You're doing whatever you can, but there's not much you can control at that point, really. … Once you have the first patient, then you don't know. You have to get 10 days past anything before you feel comfortable. Once it happens, you realize it can happen again every day.”

The Giants did not immediately announce a replacement for Wood’s spot in the rotation.