Left-hander Clayton Richard signed as a free agent, two days after being designated for assignment, and will work out of the bullpen.
Soriano, who has 207 career saves, is 2-0 with a 6.35 ERA in six games for the Cubs after signing as a free agent June 9.
''This will give him a chance to get right and then come back strong in September,'' Chicago manager Joe Maddon.
Richard elected to become a free agent after being designated then re-signed with the Cubs. He was 2-0 with a 4.29 ERA in four games for them, including three starts.
The Cubs have 39 players on their 40-man roster.