"It's very comparable to last year, as far as the baseline, so I don't think it's too serious," Roberts said. "It's disappointing, but to know he will be back to help us this year is encouraging. The great ones can do things that are essentially super human and can grind and still find ways to be great."
The Dodgers have 80 percent of the regular starting rotation on the disabled list, with Kershaw joining Rich Hill (finger blister), Kenta Maeda (strained right hip) and Hyun-Jin Ryu (pulled groin muscle). Alex Wood remains active, but he has been dealing with hamstring cramps in recent starts.
"It absolutely won't destroy us," Roberts said. "It's not ideal. Missing 80 percent of your starting rotation at some point, the shortstop, and it goes on and on. We have guys to plug in and it gives guys runways."
Kershaw had an MRI and an anti-inflammation injection on Friday after coming out of Thursday's 2-1 Dodgers loss after five innings because of back tightness. He had been activated on Thursday after missing a month with left biceps tendinitis.
To replace Kershaw on the active roster, right-handed pitcher Brock Stewart was recalled for the fifth time this year.
After Thursday's game, Kershaw compared his current back injury to last year's, which was also diagnosed as a lower back strain. His 2016 back injury was diagnosed as a herniated disk, and he missed two months. Roberts said the current injury does not involve the disk.
Kershaw, whose fastball velocity has been down several miles an hour since Spring Training, regressed further on Thursday, leading to his removal after 62 pitches in his first start since May 1. Roberts said the injury was "a byproduct of the pitching."
Kershaw, who debuted in 2008, missed a week late that season with a separated non-pitching shoulder, but he avoided the DL until sustaining a strained teres major muscle pitching the 2014 season opener in Australia. He also has dealt with hip soreness, but had generally been able to manage the condition.
Including that stint, this is Kershaw's fifth visit to the DL in the past five seasons.
Roberts would not speculate on how Kershaw would be replaced in the rotation. He's already inserted rookie Walker Buehler and reliever Ross Stripling into the rotation and has two more candidates in Stewart, who started on Monday, and Dennis Santana, who was called up earlier in the week.
"Your best player being down, it stinks," Roberts said. "I'm more sympathetic to Clayton. For him to not be with teammates and be active, he takes it a lot harder than we do."