Infante has missed the Royals' last five games because of back inflammation and Johnny Giavotella was called up from Omaha to replace him at second base in the past three games at Seattle.
"It's nothing bad," Infante said. "They think it's something muscular. I'm just feeling it there [in the lower back] and not feeling it in my leg. I feel in just the one spot."
Infante went to Kauffman Stadium on Monday's open date and tried taking some ground balls, but his back knotted up.
"He was feeling good, taking some swings in the cage," manager Ned Yost said. "Then, after 10 ground balls, it got real tight on him again and spasmed back up. We made the decision to go ahead and inject him [with cortisone], but he's still stiff and still experiencing back spasms. We're looking at it being another five days and we just felt we'd get protection on the infield."
Ciriaco was the best available option at shortstop to back up Alcides Escobar. Infante had been the fallback option to play shortstop.
The Royals' bullpen is short one pitcher, but the club opted to bypass calling up a reliever in favor of Ciriaco.
"We wanted somebody that could protect Escobar at short and also play second," Yost said before Tuesday night's game against the Rockies. "We can always go get a pitcher if we need it. I don't need it today, I've got [Danny] Duffy in the 'pen."
Duffy, though, is also scheduled to be the starting pitcher on Saturday against the Orioles so his availability is limited.
Giavotella was 2-for-11 in his three games at Seattle and his three-run homer proved to be the deciding factor in Sunday's 9-7 victory over the Mariners.
Ciriaco had a .305 average in 19 games for the Storm Chasers with eight extra-base hits and nine RBIs. He played in one game early this year for Kansas City. Over five Major League seasons with the Pirates, Red Sox, Padres and Royals, Ciriaco has been in 164 games and hit .277.
Infante, in his first season with Kansas City, has a .267 average and a team-high 19 RBIs in 30 games.
The disabled-list assignment was back-dated to Wednesday and Infante is confident his back will be OK by May 23 when he could be activated.
"It's happened to me before," Infante said. "Hopefully, I'll feel better in a week."