Erceg (hand) is dealing with soreness and swelling but is considered day-to-day, Joel Goldberg of Bally Sports Kansas City reports.
Erceg recorded his eighth save of the season in the first game of Monday's doubleheader sweep of the Guardians, walking one batter in a scoreless ninth inning.
Erceg gave up a hit and struck out one in a scoreless ninth inning Friday to record his seventh save of the season in a 7-4 win over the Phillies.
Erceg picked up the save over the Angels on Wednesday, striking out two over a perfect ninth inning.
Erceg did not allow a baserunner in 1.1 innings to earn his fifth save of the season Wednesday against the Twins. He did not record a strikeout.
The Royals acquired Erceg from the Athletics on Tuesday, Jeff Passan of ESPN.com reports.
Erceg (2-3) took the loss against the Angels on Sunday, allowing four earned runs on two hits, a walk, a hit batsman and a wild pitch without retiring a batter.
Erceg was credited with his 11th hold in a win over the Red Sox on Wednesday, firing 1.1 scoreless innings during which he allowed a hit and a walk while recording a strikeout.
The Athletics activated Erceg (forearm) from the 15-day injured list Wednesday.
Erceg (forearm) threw a successful bullpen session Sunday and is in line to be activated during the Athletics' upcoming road trip that begins Monday, MLB.com reports.