BALTIMORE -- The Giants will use Monday’s off day to make a minor rotation shuffle, pushing Drew Pomeranz’s next start back and tapping rookie Shaun Anderson to pitch against the Mets Thursday on normal rest.

Manager Bruce Bochy said Pomeranz will be available to pitch out of the bullpen Sunday if needed, as the 30-year-old left-hander threw only 56 pitches in a disastrous outing against the Orioles on Friday. Pomeranz has posted an 8.08 ERA over 10 starts this season, but Bochy said he remains in the rotation and could make his next start this weekend against the Dodgers, whose lineup skews left-handed.

“I know you look at Pom's outing, but we made that call before,” Bochy said Sunday. “We were going to switch those two to give Pom a little more time.”

“I don’t know what we’re going to do past New York right now,” Bochy said. “We’re talking about it.”

Pomeranz allowed a career-high eight runs over 1 1/3 innings in the Giants’ 9-6 loss to Baltimore on Friday night, and he has produced just one quality start this season. His rough showing capped an awful month for the Giants’ rotation, which logged an MLB-worst 7.32 ERA in May, the highest in any single month since the club moved to San Francisco in 1958.

Madison Bumgarner, Jeff Samardzija and Pomeranz are the only members of the Giants’ Opening Day rotation still standing, as the rest of the staff’s struggles have created openings for Anderson and Tyler Beede to get looks with the club.

Posey exits with hamstring injury

Buster Posey left Saturday's game after developing right hamstring soreness in the seventh inning. Posey, who started at designated hitter, tweaked his hamstring while attempting to beat out a grounder in his final at-bat of the game against Orioles right-hander Miguel Castro. He was replaced by Tyler Austin in the ninth.

Bochy said Posey is considered day to day. He isn’t expected to start Sunday’s series finale, but he could be available to pinch-hit. The Giants are hoping he’ll be able to return to action on Tuesday in New York.

Williamson elects free agency

Mac Williamson’s tenure with the Giants is officially over. The 28-year-old outfielder cleared waivers and elected free agency Saturday after being designated for assignment last week. A third-round Draft pick of the Giants in 2012 out of Wake Forest, Williamson spent parts of five seasons with the club, batting .207 with a .641 OPS in 357 Major League at-bats.

He was hitting just .118 with 18 strikeouts in 51 at-bats when the Giants opted to cut him and promote Mike Yastrzemski from Triple-A Sacramento. Because he had already been designated for assignment once earlier this season, Williamson had the option to decline an outright assignment and depart the organization as a free agent once he cleared waivers.

“I pull for Mac,” Bochy said. “I wish him the best. I thank him for all that he did here. He came up as a Giant. Unfortunately, it didn’t quite work out like we had hoped. I think he’s got baseball left. Sometimes a change of scenery can do a player a lot of good. This guy has got tremendous potential.”

Coaching shuffle

Curt Young underwent surgery on his right knee Friday and is expected to be out for a while, leaving Matt Herges as the acting pitching coach. The Giants added Triple-A pitching coach Steve Kline to their staff to serve as the interim bullpen coach.