Clayton Kershaw's back, which landed him on the 10-day injured list four hours before he was scheduled to throw the first pitch of the Los Angeles Dodgers' season on Thursday night, is progressing well enough to make him believe he won't be sidelined much longer.

Kershaw said Friday that the injury, classified by the team as stiffness, is "not too serious" and "getting better pretty quick," adding that he is "optimistic" he will return shortly after he is first eligible to next Friday.

Kershaw's back originally stiffened up while he went about his normal routine in the weight room Tuesday, but an MRI later that day came back clean. He received treatment over the next couple of days but couldn't get his back loose enough to make his first start. Dustin May replaced him, holding the San Francisco Giants to one run in 4 1/3 innings, and will probably start again during next week's road trip.

Kershaw played catch from 90 feet on Friday and said he is "somewhat thankful that it's not super serious." The 32-year-old left-hander has now been sidelined by back injuries four times over the past five years. His latest issue came moments before what would have been his ninth career Opening Day start.

"Obviously the timing couldn't have been worse, working all that time to try and stay ready" Kershaw said. "I felt so good going into this season. It was pretty defeating, honestly. Just like, 'How is this happening now?' But I kind of started moving forward yesterday and today made a lot of progress."