This isn't the first time Freeman suffered a thumb injury in his career. In the second preseason game of the 2010 season he suffered a minor fracture, which prevented him from playing in the final two preseason games and noticeably bothered him early on in the 2010 season. Through the first three games of that season he completed 59% of his passes for just 6.6 yards per attempt, four touchdowns and two interceptions. After the bye week Freeman was back to normal and much more accurate.
His current thumb injury doesn't appear to be as serious. He hasn't been limited in practice, and the Tampa Bay Times reports that he has looked normal in practice. And to be fair, it's not like Freeman has been extremely accurate this season anyway. But if you start seeing some extra off-target balls on Sunday, maybe that's caused by this minor injury.