When Matt Cassel(notes) hobbled to the trainer's room Saturday, the air was sucked out of Arrowhead Stadium. The Chiefs' most heralded offseason acquisition was injured, and the pattern of 2008 seemed to be repeating itself. Chiefs officials weren't spilling much about what ails their starting quarterback, only that he had injured a leg and wouldn't return to their exhibition against the Seahawks. Writing for the Kansas City Star, Kent Babb put it this way:"Cassel's injury was something Kansas City couldn't afford. He was more valuable than the $28 million guaranteed contract he signed two months ago—he was the future. Cassel was supposed to be the quarterback the Chiefs had waited decades for. And even if he couldn't become Len Dawson, then he at least wouldn't be Brodie Croyle(notes) or Damon Huard(notes)."Word could come Sunday that would render this handwringing moot, but the mood in KC went from bad to worse when Cassel went down.For the record, Cassel was tackled from behind by Seahawks defensive tackle Brandon Mebane(notes). He clutched his left leg while down. After struggling to get back to the huddle, Cassel called time out and limped off the field.Tyler Thigpen(notes) replaced Cassel and could wind up as the Chiefs' Week 1 starter if Cassel's injury KO's him.The bad news didn't end with Cassel. Wideout Devard Darling(notes) and cornerback Brandon Flower also were injured.