Flaherty (3-0, 2.25 ERA at Triple-A) will have time to throw a second between-start bullpen and join the team in Pittsburgh.
The Cardinals have not yet announced a starter for Saturday, in part, because what happens in the three games against the Mets could force other roster decisions on them. An injury or an extra-inning game could require an adjustment to the plan. The Cardinals also want to avoid making the roster move until necessary.
The team has three pitchers on the 40-man roster who are all pitching well and could all be available, if needed, for Saturday: Flaherty, Austin Gomber, and John Gant.