Anderson Silva was injured going into the fight

In an interview, Silva's Manager, Ed Soares talks about how Anderson was injured sparring Lyoto Machida;

"It was really close because the doctors didn't want him to fight. He hurt his rib last Friday in sparring. He hurt it, but he didn't think it was hurt that bad and then Sunday morning, I had about 13 missed calls in a matter of 25 minutes. They were all from Anderson and he was calling me to tell me he was in pain. He couldn't breathe. I took him to the hospital and they X-Rayed each rib and they noticed that it was a bit swollen, but there was no fracture. They said it was bruised ribs, but the way he reacted when they touched it and how tender they were, they said it was in the muscle as well as the bruise. I'm not a doctor, but this is just what they told us. They prescribed some Ibuprofen 800 for him because it was so close to the fight, they couldn't do any Vicodin.

The doctors said, "I really don't recommend that he fights," but Anderson said, "No man, the show must go on. I'm going to fight." I put it this way, he was supposed to corner Mark Munoz on Sunday for his fight against Okami, but I made him stay at home in bed. He was just lying around and letting his ribs heal up on Sunday, Monday and Tuesday because we traveled. He didn't train again until we got to Oakland. He gave his ribs about a 5-day rest."

And then asked about a rematch with Sonnen, Soares comments;

"I mean, I don't necessarily think an immediate rematch is legitimate. It's not like he won by decision. You got submitted, man. You were on top of him for 23 minutes of the fight and you couldn't finish him. Anderson got a few bumps and bruises, but let's be realistic, you're on a guy 23 minutes and you couldn't finish him? Why should he get a rematch?"

[source]