Santana suffered the injury in his last start before the All Star break on July 6, a game in which Justin Turner started at first base, when Reed Johnson stepped on Santana's ankle at first base. He pitched through the rest of that start and two starts after the break to disastrous results. In the three starts, he lasted just 12.2 innings in total and posted a 13.50 ERA. The Mets say that the injury has everything to with his ankle and nothing to do with his surgically-repaired shoulder.
While it's easy to break Santana's season into two parts — through his no-hitter and post-no-hitter — his numbers since the historic game are heavily skewed because of his last three starts.
For now, it looks like the Mets' current rotation is: R.A. Dickey, Jon Niese, Chris Young, Miguel Batista, and Jeremy Hefner. The team will obviously miss Santana and Dillon Gee, and Matt Harvey could very well find himself on the big league roster in the near future.
Unfortunately, putting Santana on the DL turned out to be the roster move that made room for the recently recalled Hefner.