Riggins told ESPNChicago.com that he was waiting for Garza to be cleared by team orthopedic specialist Stephen Gryzlo in order to be able to play catch on Sunday. The plan was that if Garza came through that OK, he would throw a side bullpen session later in the week in hopes of preparing for a start this weekend.
Garza was retroactively placed on the 15-day DL May 18. He will be eligible to rejoin the active roster June 3, when the Cubs start a three-game set against the Cardinals in St. Louis.
Garza, with a 3.72 ERA, is leading the NL with 10.99 strikeouts per nine innings. He is the third member of the Cubs' starting rotation to hit the disabled list this season.
Riggins also confirmed that after throwing a side session Saturday, newly acquired pitcher Rodrigo Lopez will start for the Cubs Monday.
Sahadev Sharma covers the Cubs and White Sox for ESPNChicago.com.