Brown didn't practice Thursday due to a knee issue, Jim Wyatt of the Titans' official site reports.
Brown wasn't listed on Wednesday's injury report, but it's possible that his absence is simply rep management, given that he missed time earlier this season with a bone bruise in his knee. If the wideout's absence Thursday is indicative of a setback, however, Friday's practice/injury report should add clarity on that front one way or the other.