Reds manager David Bell said Castillo (shoulder) will play catch Thursday and is likely to throw a bullpen session over the weekend, Mark Sheldon of MLB.com reports.
Cincinnati officially moved Castillo to the 10-day injured list Thursday, but the right-hander doesn't look like he'll reside there for a lengthy period to open the season. Though Castillo isn't on pace to make it back on the active roster in the minimum 10 days, Bell said that the Reds are optimistic the 29-year-old will be ready to go by late April. While Castillo and Mike Minor are on the IL, top prospects Hunter Greene and Nick Lodolo will hold down spots at the back end of the rotation.