The 35-year-old right-hander threw about a 30-pitch bullpen session for the second time in three days on Friday. He plans to throw again on Monday, then make one or two rehab starts before returning from the 10-day disabled list.
Shields has been sidelined since April 16 by a strained right back muscle. Coming off a rough first season with Chicago, Shields is 1-0 with a 1.62 ERA in three starts.
Chicago also placed struggling rookie Dylan Covey (strained left oblique) on the 10-day DL and recalled right-hander Juan Minaya from Triple-A Charlotte. Covey is 0-4 with an 8.12 ERA in eight starts.