Kazmir, who had been in line to be the team's fourth or fifth starter for this season, threw 71 pitches, with only 44 strikes, and his velocity was recorded at 82-84 mph during the session. His velocity last season averaged in the low 90s.
"We've still got to see some improvement in the velocity at some point in time," Roberts told reporters. "And I think he'll say the same thing. I don't know if there's a certain number of miles per hour that he needs to pitch at. I think he was 82-84 today. ... That's not the number, and he'll be the first to tell you that."
Kazmir, who said he's been dealing with hip issues since last season, remained confident after the outing, but he knows his velocity isn't where it needs to be.
"I feel close, really close," Kazmir told the Orange County Register. "I was able to keep my tempo, keep my balance and use this hip to get through. It's a lot of things that we have to focus on. It's just a matter of putting that all together.
"I don't even want to know [about the velocity]. I know it's not there yet."
Kazmir had an MRI on March 8 after feeling soreness in his left hip, but it came back clean. He also missed a month last season with neck inflammation and back issues. He has been working with pitching coach Rick Honeycutt to improve his mechanics.
"From everything I hear, he's healthy," Roberts said. "The next step is, if he can feel good about that, hopefully the velocity ticks up. ... He feels strong, but it's still not coming out the way we need it to right now."
The club's top three pitchers are set in Clayton Kershaw, Rich Hill and Kenta Maeda. After that, Kazmir was in a large group vying for one of the final two spots along with Brandon McCarthy, Hyun-Jin Ryu, Julio Urias, Brock Stewart, Ross Stripling and Alex Wood.
ESPN's Doug Padilla contributed to this report.