Horton didn't practice Monday, with coach Mike Macdonald saying the wideout is "working through some things" at the moment, Gregg Bell of the News Tribune reports.
Horton was a full participant during the first week of training camp, after having a metal rod put in his lower leg in February to stabilize the shin fracture that ended his rookie season. He didn't play in Seattle's preseason opener, and he's now absent from practice as the team begins preparing for the second exhibition. It's unclear if Horton's current problem is related to the offseason surgery.