USC wide receiver Marqise Lee had a surprising slide out of the first round on Thursday. Now we know why he tumbled.

On Friday, rumored Eagles wide receiver target Marqise Lee fell out of the first round, which surprised a lot of pundits and fans. However, Lee was passed on mostly due to the knee injury that hampered him throughout his junior year, according to TFY Draft Insider Tony Pauline. The left knee injury made Lee's production drop significantly from his sophomore to junior seasons.

Lee was widely considered a Top 5 receiver in the draft and still could be that fifth receiver taken, as just Sammy Watkins, Mike Evans, Odell Beckham and Brandin Cooks were selected in the first round. Lee will likely go early on Day 2 but the knee injury clearly hurt him with teams. It is unclear the extent of his knee injury, but teams clearly didn't feel comfortable taking him too early due to its condition.