The Reds said earlier this week that Gonzalez was expected to miss the first few spring training games because of a sore knee. An examination by team physician Dr. Timothy Kremchek revealed the break.
Gonzalez hit .272 with 16 homers and 55 RBIs in his first season with the Reds. He didn't start a game after Sept. 12 because of a bone bruise in the same knee.
The team said the fracture is unrelated to the injury that Gonzalez sustained last year.
"There are four or five guys that are affected," manager Dusty Baker said.