Kemp, who has been rehabbing a left ankle sprain, experienced some hamstring tightness while running the bases Thursday at the Dodgers' minor league facility in Glendale, Ariz. Kemp spent a month on the disabled list earlier this summer with a mild strain of the same hamstring.
"I don't like to concede anything really," Mattingly said. "But [when] the hamstring kind of jumps back in there and becomes involved, that means we have more issues.
"Obviously at some point we run out of time."
Kemp, who is hitting .263, hasn't played for the Dodgers since July 21. In a recent five-game rehab assignment with Single A Rancho Cucamonga, Kemp went hitless in 18 at-bats with seven strikeouts.