"My knee is banged up," he said.
"I've got a sprained MCL. It just got worse during the week. So I was just trying to come out and play and try to help the team but just didn't feel well today."
Pryor, who played with a brace on his leg, initially sprained the knee in last week's home loss to the Philadelphia Eagles but practiced this past week with no hindrance. And yet, it was obvious against the Giants he was not himself.
"I couldn't get any push-off on my leg," he said after completing just 11 of 26 passes for 122 yards with an interception and a lost fumble.
"I couldn't explode in the passing game," he said, "couldn't explode in the running game."
Pryor was sacked four times and rushed for 19 yards, a career low for a start.
Raiders coach Dennis Allen acknowledged that Pryor did not look healthy.
"I think we all could watch from the sideline and tell that it didn't look like he had the same explosiveness," Allen said, "but that wasn't something that we noticed going into the week."
The only other quarterback on the Raiders' active roster is undrafted rookie Matt McGloin out of Penn State, while fourth-round draft pick Tyler Wilson is on the practice squad. The Raiders worked out veterans David Carr, Trent Edwards and Pat White last month.