"It was pretty much both, the knee and I was sick," Clowney revealed on Wednesday, according to the Houston Chronicle. "I was out. I didn't get to practice at the end of the week. I was at home sick.
"I don't know what I had, but it wasn't good. I'm feeling better. The knee is getting better."
Clowney has appeared in just one game since undergoing surgery to repair a torn meniscus in his knee after Week 1. He admitted Wednesday he still feels discomfort when he moves laterally.
"There are certain things going on with my knee still," he said. "I'm not able to do the things I want to do. It's just not where it needs to be right now. We're taking a step back and trying to get it to where we need it be so I can play."
This is beginning to look like an ailment that will plague Clowney for the balance of his rookie season. It also puts the Texans in a predicament: They want their prized rookie to continue his development on the field, but they also must be wary of any long-term effects of playing him at less than 100 percent.
Perhaps Clowney will be fully recovered in a few weeks. But it's also possible that the rookie gets shut down if Houston falls out of the playoff picture entirely.