According to Matt Maiocco, Joshua Morgan fractured his right ankle when Bucs cornerback Anthony Gaitor tackled him with 4:46 left to play in the 4th quarter and the Niners winning by 38 points.
It was a 4th and three from Tampa Bay 20 yard line, and Harbaugh elected to go for the first down instead of the field goal. Everyone in the press box was talking about this decision after the game. It seems obvious that he should have kicked the field goal up that many points.
Still, players can get hurt on a field goal attempt as well. As Harbaugh says, you have to play the game.
The Niners will only have three healthy wide receivers on the roster next week: Michael Crabtree, Ted Ginn Jr., and Kyle Williams.