SAN FRANCISCO -- The injuries are beginning to pile up for the struggling Giants, who saw another position player go down in a 4-2 series-opening loss to the Reds at Oracle Park on Friday night.

With Jung Hoo Lee nursing a sore left foot, the Giants tapped Austin Slater to make his second consecutive start in center field, but he ended up leaving the game with concussion-like symptoms after slamming into the center-field wall on an attempted catch in the first inning.

Slater was slow to get up after crashing into the fence on Spencer Steer’s RBI double off Logan Webb, and was later seen walking down the dugout steps with head athletic trainer Dave Groeschner. The Giants sent Michael Conforto to pinch-hit for Slater in the bottom of the second, with Tyler Fitzgerald sliding over to play center in Slater’s stead.

It’s been a wretched start to the season for the 31-year-old Slater, who has batted only .128 with zero extra-base hits over his first 49 plate appearances of the year. The Giants were hoping Slater would be able to get going after facing Cincinnati lefties Andrew Abbott and Nick Lodolo in the first two games of this series, but manager Bob Melvin said there’s a “good chance” the right-handed hitter will be placed on the seven-day concussion list on Saturday.

Outfielder Luis Matos and infielders Marco Luciano and Brett Wisely could be among the candidates to be called up from Triple-A Sacramento as a corresponding move, though Slater’s injury could also create some more playing time for Heliot Ramos, who went 2-for-4 with a double in his third game since being recalled on Wednesday.

“He’s swinging the bat well,” Melvin said of Ramos. “What we saw in Triple-A, he’s brought here. He’s getting good, competitive at-bats almost every time up, hitting the ball hard. It’s nice to see him come up and contribute a couple more hits tonight. He’ll be in there tomorrow.”

The Giants already have catcher Patrick Bailey on the seven-day concussion list, though he is on track to return on Saturday if he clears concussion protocol before the game. They’re expected to be without designated hitter Jorge Soler (right shoulder strain), catcher Tom Murphy (left knee sprain) and shortstop Nick Ahmed (left wrist sprain) for a bit longer, further depleting a lineup that has averaged only 2.87 runs per game over its last 15 contests, the second-lowest mark in the Majors behind the Pirates.

Coming off a nightmarish 3-7 road trip to Boston, Philadelphia and Colorado, the Giants were hoping they’d be able to get back on track at home against the reeling Reds, who entered Friday having lost eight in a row, but San Francisco couldn’t build on the early momentum it showed against Abbott.

The Giants went ahead, 2-1, after Thairo Estrada launched a first-inning homer and Ramos doubled and scored on Fitzgerald’s single in the second, but they were blanked the rest of the way en route to their eighth loss in 11 games.

“We just lost our mojo along the way somewhere,” Melvin said. “We had good at-bats early in the game. We give up a run and then we get it right back. We score another one in the second, it feels like we’re on our way to having a pretty good offensive night. And we couldn’t do anything to sustain it after that. With us right now, we’re not hitting the ball out of the ballpark. We’ve got to be able to sustain some at-bats and put some pressure on. Other than the home run that Estrada hit, we just couldn’t do it after that.”

The Giants couldn’t support a solid start from right-hander Logan Webb, who gave up three runs (two earned) on eight hits over seven innings. Webb struggled in his previous two outings against the Red Sox and Phillies, but he managed to minimize damage early against the Reds and ended up retiring nine of the final 10 batters he faced.

“I thought it was a step in the right direction,” Webb said. “Still not good enough, but I thought my velo was back up a little bit. I thought the shapes were good on some pitches. But it’s been a tale of two games early on. Not very good, figured it out late, and at that point, it’s too late. I’ve got to be better.”

Webb departed with the Giants trailing, 3-2, though the Reds tacked on an insurance run when Stuart Fairchild delivered a pinch-hit, inside-the-park homer in the eighth. The Giants’ ace didn’t mince words when asked to describe the team’s poor stretch of play after the game.

“It’s [crap], to be honest, as a whole,” Webb said. “It’s frustrating. It’s not good enough.”