LOS ANGELES -- Only a few hours before his scheduled Opening Day start, Clayton Kershaw was placed on the 10-day injured list with back stiffness and rookie Dustin May -- who was sent down earlier in the day -- was recalled to start Thursday's opener against the Giants.

May delivered in his start, allowing one run over 4 1/3 innings while hitting triple digits with four strikeouts in the Dodgers' 8-1 win at Dodger Stadium.

“He’s unflappable,” manager Dave Roberts said of May. “To get the ambush notice the day before Opening Day, it was fun to watch.”

Meanwhile, Kershaw has a history of back injuries, putting him on the injured list in 2016, '17 and '18, but he seemed healthy throughout Summer Camp and pitched 6 1/3 innings in a final intrasquad tune-up six days ago.

Roberts said Kershaw was injured on Tuesday working out in the weight room. The Dodgers remained hopeful he could start the opener, but the club “erred on the side of caution” because it wasn’t “prudent to start him.” Roberts said Kershaw felt improvement with treatment over the last few days.

Roberts did not have a timeline for Kershaw’s return, but the lefty's placement on the injured list was backdated and he’ll be eligible to return during next weekend’s series in Arizona. The three previous times Kershaw has been on the injured list with back injuries, he missed 10 weeks, five weeks and three weeks, respectively.

“We’re not going to compromise anyone’s health,” said Roberts. “Once he’s ready, he’ll pitch for us.”

Roberts said he gave May a heads-up on Wednesday to the possibility he would start and canceled his scheduled simulated game. The 22-year-old May became the first rookie to start on Opening Day for the Dodgers since Fernando Valenzuela in 1981.

“When a change in plan happens, Dustin adapts very well,” said Roberts.

Kershaw’s injury further depletes a starting rotation that already lost another former Cy Young Award winner, David Price, who elected not to play this year. In addition, veterans Hyun Jin Ryu, Kenta Maeda and Rich Hill are no longer with the club.

The rotation now includes Ross Stripling, a 2018 All-Star as a sub starter; Julio Urías, in a make-or-break trial as a starter; and Alex Wood, who returned from Cincinnati after winning only one game with the Reds in a season plagued by a bad back. Co-ace Walker Buehler threw a four-inning simulated game on Wednesday, and he is scheduled to make his first start on Tuesday in Houston after falling behind in his Summer Camp buildup.

This is the second consecutive Opening Day start Kershaw has missed because of injury. He missed last year’s opener with a sore left shoulder, but he ultimately healed and went 16-5 with a 3.03 ERA.

“The disappointment for me is for Clayton. He’s the most prepared player I’ve ever been around,” said Roberts. “Starting an Opening Day means a lot to him.”