Moustakas declined a $15 million mutual option on Tuesday.
He rejected a $17.4 million qualifying offer and left Kansas City after the 2017 season but was unable to find a long-term deal he liked. He returned to the Royals in mid-March for a one-year contract that included a guaranteed $6.5 million: a $5.5 million salary and $1 million option buyout. Moistakas earned an additional $2.2 million in performance bonuses based on plate appearances, raising his total earnings for 2018 to $8.7 million.
A 30-year-old left-handed hitter, Moustakas had a .251 average with 28 homers and 95 RBI. He hit .256 with eight homers and 33 RBI in 54 games for Milwaukee, which acquired him from the last-place Royals on July 27.
Soria declined a $10 million mutual option and gets a $1 million buyout, completing a $25 million, three-year contract he agreed to with the Royals in December 2016. The right-hander was acquired from the Chicago White Sox on July 26 and was 3-1 with a 4.09 ERA in 26 games with the Brewers.