Wells and Andrew Cashner, the Cubs' fourth and fifth starters, were placed on the disabled list on April 8 after each made one start. Cashner is still out with a right rotator-cuff strain.
Both pitchers have been rehabbing at the Cubs' minor league complex in Mesa, Ariz.
The Cubs have struggled to fill the void at the back of their rotation. Casey Coleman and James Russell have been ineffective, and the team signed veteran Doug Davis to a minor league contract. Davis will replace Russell and makes his first start on Saturday against the San Francisco Giants.
ESPNChicago.com's Bruce Levine contributed to this report.