Patriots safety Patrick Chung underwent surgery on his right thumb this week after injuring it Sunday against the Chargers, according to two sources. He did not practice Wednesday and his availability going forward hasn't been determined. Chung, a 2009 second-round draft pick, injured the right thumb in the third quarter of Sunday's game. The injury appeared to occur on a third-down play in which he jammed tight end Antonio Gates at the line of scrimmage.