Santana was placed on the 10-day injured list Friday with a right intercostal strain. The move is retroactive to Sept. 28.
It's unclear exactly how long the right-hander has been dealing with the injury, as his only appearance in the past three weeks came on Sept. 20. Since the move is backdated, Santana will be eligible to be activated for the first game of the NLDS next Friday, though it's unclear if he's expected to be healthy by that point.