It will be the first game Ryu has pitched since he came out early on Sept. 9 because of left shoulder irritation. It also will be his first career road playoff start.
Ryu will be on an estimated pitch count of 100-110.
''That, obviously, would depend on how he gets there, if there's a bunch of battles trying to get there and how he's pitching,'' Mattingly said. ''But we don't feel like he's lost a ton of arm strength. He's been through this once before -- I think he missed 21 days or something, came back and threw really well.''
The Dodgers had yet to release their playoff roster by late afternoon. The deadline is Friday morning.
Ryu pitched a three-inning simulated game Wednesday to show his readiness.
To read more on the upcoming matchup between the Dodgers and Cardinals, visit FOXSports.com