According to ESPN, Theo Walcott has sustained a chest injury sustained after the San Marino goalkeeper Aldo Simoncini tackled the winger, hard, after Walcott had lifted the ball over him:

Theo Walcott has been taken to hospital with a chest injury sustained against San Marino

— ESPN FC (@ESPNFC) October 12, 2012

The exact nature isn't clear and hasn't been diagnosed yet, so whether it's just bruising, broken ribs, or maybe just really bad heartburn from some particularly fresh gyros is not yet known. Hopefully nothing is broken and Walcott will be able to return to action soon, just like Laurent Koscielny. [Ed. note: please, please, take it easy with our freshly injured players, though, England, and France, and every other nation. Thank you.] In the meantime, Alex Oxlade-Chamberlain will probably be spelling Gervinho on the right side of Arsenal's attack, as Theo makes about the thirtieth Arsenal player to sustain an injury playing in a nineteenth-century geopolitical history lesson.

Yay.