"I say 10 days to two weeks would be fair," Hillman said.
Soria threw before Saturday's game, both from various distances and from the mound under the supervision of athletic trainer Nick Swartz.
"[Soria threw] 25 throws off the mound, all pitches, not max effort but he was spinning them," Hillman said. "He said he didn't feel anything in the shoulder."
On Sunday, Soria will play catch, but Hillman was not ready to say when he might be ready for a full session in the bullpen.
"He's making progress," Hillman said. "We're being cautious, obviously, but Nick's letting him having some ownership from the standpoint of he's got to tell us how his body feels. We've got to go off of that."
"At the same time, when we get him back, I don't want to be flipping a coin on whether we're going to have him a couple days in a row. We'd like to have him at full tilt at that point."
Hillman reiterated that Soria will have an injury rehabilitation assignment in the Minor Leagues before returning to pitch for the Royals.
Soria had seven saves in seven opportunities with a 1-0 record and 2.08 ERA in eight games. In his last outing against Seattle on May 7, he needed 29 pitches to get through seven batters but gave up only one run and got the save. He had been bothered by shoulder soreness since at least April 14, although the Royals did not make it public until April 24.
Entering Saturday, the Royals are 0-for-4 in save opportunities since Soria was sidelined, with Jamey Wright, Juan Cruz, Sidney Ponson and Horacio Ramirez each blowing one save.
Dick Kaegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.