Williams (abdomen) threw a bullpen session Thursday and could rejoin the team soon.
Williams threw a simulated inning Tuesday and ramped up his activity two days later. Manager David Ross said he wants to build up the righty's innings before he rejoins the team, but that could happen in the next few days. Williams could bump Alec Mills to the bullpen when he returns, though the Cubs may stay somewhat fluid with the No. 5 spot in their rotation to manage workloads this season.