ESPNNewYork.com's Adam Rubin is reporting via Twitter about Santana heading to the DL:
Johan Santana to DL, officially with ankle injury.— Adam Rubin (@AdamRubinESPN) July 21, 2012
There were concerns from around the majors that Santana was going too hard too soon after having shoulder surgery, but the pitcher's recent struggles don't appear to be related to that previous injury.
Just as Rubin stated, the belief is that any other soreness in his shoulder or any missteps in his delivery can be attributed to the sore ankle.
What It Means
The New York Mets sit 4.5 games out of one of the NL wild-card spots, and losing Santana may be too big of a blow for the talented team to overcome.