Moore disclosed that Guillen has a partial tear of the right hip flexor and is expected to return after the 15 days.
"Jose wanted to play through it, but this is the right thing to do for him and the team," Moore said.
Guillen appeared to pull up while running out a ground ball in the ninth inning on Thursday at Chicago, where he served as the designated hitter.
Moore said the Royals did not want to take the risk that Guillen, playing in early-season cold weather, might worsen the partial tear in the hip and risk months out of the lineup or possibly surgery.
The Royals had to make room on the roster for starting pitcher Sidney Ponson, who was pulled up from the Triple-A roster to start Friday's home opener against the New York Yankees. Guillen's move to the disabled list apparently kept third-string catcher Brayan Pena on the Royals' roster.
Guillen was not listed in the starting lineup on Friday and, for his part, he played innocent when asked on Friday morning if he was hurt.
"Me? Nooooo!" he said. "I'm fine."
But why wasn't he in manager Trey Hillman's lineup?
"Don't let the lineup fool you, I might be there later on, before the game starts," Guillen added.
But later Hillman told reporters that Guillen was "sore" in his right hip. About an hour later, Moore revealed that he was on the disabled list.
The absence of Guillen had a domino effect on the Royals' lineup against left-hander Andy Pettitte.
Mark Teahen moved into Guillen's usual spots as cleanup hitter and right fielder. David DeJesus took the third spot in the order where Teahen had been. Alberto Callaspo took over second base from Teahen.
"We have changes," Hillman said. "It certainly affects when you take a right-handed bat out and have a lot of left-handed hitters on your roster. We've got some guys who have some decent histories against Mr. Pettitte so we'll see how that plays out for us."
Guillen often played last season with leg injuries but did not go on the disabled list.
This spring, he reported to Spring Training with an ingrown big toenail, which he yanked out himself. He also was bothered briefly by a sore shoulder, then went off to play in the World Baseball Classic.
"But once he got back from the Classic, his body was feeling really good," Hillman said.
Before it was revealed he was on the DL, Guillen continued with his banter.
"I'm fine, I'm going to hit a walk-off homer today," he said.