LOS ANGELES -- Clayton Kershaw has been scratched from his scheduled start in the Los Angeles Dodgers' opening game on U.S. soil against the San Diego Padres on Sunday after an MRI showed inflammation in a muscle in his back.

The two-time Cy Young Award winner said he did not believe the injury to the Teres muscle in his back was serious, and he said he is looking at it like he's simply pushing back a start, rather than missing one. Still, his frustration was palpable.

Clayton Kershaw had an MRI on Wednesday that showed a swollen muscle in his left upper back. Cameron Spencer/Getty Images

"It's nothing that I'm too worried about. It's really frustrating more than anything. The timing of it," said Kershaw, who pitched the Dodgers to a 3-1 victory over the Arizona Diamondbacks on Saturday during the teams' opening series in Australia.

"It's just one start that has to be pushed back. It's definitely something that if I had to pitch tomorrow, I could probably do it. It just wouldn't feel great."

Kershaw said he wasn't sure how he injured the muscle but rejected the notion that it could have been caused by the shortened spring training the Dodgers had in order to travel to Australia.

"I progressed well, my pitch count increased each time, so I don't think the shortened spring had anything to do with it," he said. "I really wanted to pitch [Sunday]. It's hard to admit you don't feel right. I guess just when it was laid out to me and I understood that we have guys that can fill the spots with the off days that we have, it's almost not me missing a start, it's just going to be pushed back a few days. That helped ease it a little bit, but either way, it's not fun to deal with."

Kershaw signed a seven-year, $215 million contract with the Dodgers this winter.

Dodgers manager Don Mattingly said the team was still assessing its options for Sunday. The most likely choices are left-hander Hyun-Jin Ryu and veteran right-hander Dan Haren. The team will wait to see how Ryu responds to treatment on an injured toenail that he experienced problems with after his start in Australia. Ryu had a procedure done on the toe that seemed to alleviate some of the pain, Mattingly said.

Zack Greinke is scheduled to start Tuesday's game in San Diego and will not be moved up, Mattingly said.

"We're not overly concerned," Mattingly said of Kershaw's injury. "We just don't want to let it turn into something bigger. We've got lots of off days. We're at the very beginning of the season. And we want him, once he gets going, to stay in it."