Sweeney, the team’s home run and RBI leader, is expected to miss the next two or three days with a strained right hamstring.
The three-time All-Star suffered the injury while rounding first base on a double in the sixth inning of Wednesday’s 9-6 home loss to Boston.
“Hopefully, it’s just a mild strain,” trainer Nick Swartz said. “We’ll take it easy for a few days. Better to lose two or three days now versus losing three weeks later on.”
The news came just before the opener of this series was postponed due to tornadoes in the Kansas City area.
The Royals have lost seven of 10, including their first back-to-back home defeats of the season.
The Orioles are coming in off an embarrassing three-game sweep by lowly Detroit, capped by a 9-4 loss on Wednesday.
David Segui, who missed two weeks at the end of April with a strained right hamstring, went 3-for-3 with a homer as Baltimore lost its fourth in a row.
STANDINGS: Orioles - 3rd place, 8 GB, AL East. Royals - 1st place, AL Central.
ORIOLES PROBABLE GAME ONE STARTER: Rick Helling (1-3, 5.86 ERA). Helling has lost his last two starts, giving up 11 earned runs and 18 hits over 9 1-3 innings. In last Friday’s 5-2 loss to the Royals, Helling allowed four runs and seven hits over 5 2-3 innings. The right-hander is 5-3 with a 5.09 ERA in 11 career starts against Kansas City.
ROYALS PROBABLE GAME ONE STARTER: Miguel Asencio (2-0, 4.14 ERA). Asencio outdueled Helling last Friday in his first career start against Baltimore. The right-hander pitched the first complete game of his career, allowing two earned runs and seven hits, while striking out six. He had never pitched more than seven innings in any of his previous 26 starts.
ORIOLES PROBABLE GAME TWO STARTER: Sidney Ponson (3-2, 4.03 ERA). Ponson is 2-0 with a 2.54 ERA in his last two starts, including allowing one run and five hits over eight innings in Saturday’s 6-1 win over Kansas City. He is 3-0 with a 1.64 ERA in his last three starts against the Royals, and 6-4 with a 3.56 ERA in 11 starts against them in his career.
ROYALS PROBABLE GAME TWO STARTER: Runelvys Hernandez (4-1, 1.74 ERA). Hernandez took the loss against Ponson and the Orioles on Saturday, allowing a season-high three earned runs and seven hits over seven innings in his first career start against Baltimore. The right-hander came in with an AL-low 1.36 ERA and was looking to become the first Royals pitcher to open 5-0 since Bret Saberhagen in 1987.
OFFENSIVE LEADERS: Orioles - Jerry Hairston, .298 avg. and 12 SBs; Tony Batista, 5 HRs and 19 runs; Jeff Conine, 21 RBIs. Royals - Raul Ibanez, .313 avg.; Sweeney, 7 HRs, 26 RBIs and 19 runs; Carlos Febles, 5 SBs.
SEASON SERIES: Royals, 2-1.
STREAKS AND NOTES: Orioles - The Orioles have won six of their last seven at Kansas City. … 3B Batista has gone nine games without a homer, a span of 40 at-bats. … C Brook Fordyce went on bereavement leave Thursday after the death of his father, Tom, in Connecticut. He is expected to rejoin the team in Chicago next week. C Robert Machado was brought up from Triple-A Ottawa to take his roster spot. Royals - The Royals have been alone atop the AL Central for 31 games, their longest span in first place since leading the AL West in 1980 from May 23 on. … RHP Hernandez has limited opponents to a .187 batting average, second-lowest in the AL. … The Royals are 1-1 without 1B Sweeney this season.
ROAD/HOME RECORDS: Orioles - 8-6 on the road; Royals - 11-2 at home.
INJURIES: Orioles - RHP Rodrigo Lopez (ribcage), 15-day DL; OF Marty Cordova (elbow), 15-day DL; OF B.J. Surhoff (hamstring), 15-day DL; LHP Erik Bedard (elbow), 60-day DL; RHP Scott Erickson (shoulder), 60-day DL; OF Albert Belle (hip), 60-day DL. Royals - 1B Sweeney (hamstring), day-to-day.