Ellis underwent emergency surgery May 19 to relieve pressure from swelling in his lower left leg after a take-out slide by St. Louis baserunner Tyler Greene.
"It sounds like he's getting close to going out," said Mattingly, who added that Ellis would play four or five games with around 20 at-bats before being activated. "It seems like there's a chance of getting him back before the [All-Star] break."
The Dodgers are 22-11 with Ellis starting at second base and batting second. They are 21-21 when he isn't.
Mattingly said Kemp (hamstring) is a few days behind Ellis. Mattingly has said Kemp won't play in the All-Star Game (he's the leading outfield vote-getter) if he hasn't first returned to the Dodgers' lineup. Kemp hasn't ruled that out.