CBS Sports on their website post a listing of the NFL injury report for each week (as a means of supporting their Fantasy Football program). Marshall was posted there as being "doubtful" for the Seattle game due to his hamstring injury while also being listed as "probable" for the season opener.
There is a lot of speculation running around that Marshall's absence from the Seattle game is a sign that the rift between the Broncos and Marshall is growing. People wondering if this is a sign that there is an impending trade on the horizon. Try checking out the injury reports.
The majority of the reads that I have seen have focused on the "controversy" between Marshall and the Broncos -- that Marshall wants a bigger contract, that he doesn't trust the medical staff, that he's upset with the PR department, that there are trust issues, that he's being punished by the Broncos for his attitude, etc etc ad nauseum. Might not the explanation be, in fact, much more simple?
Marshall has been held out of practice due to a hamstring injury. Given his stated distrust of the Broncos' medical staff, might they be choosing to be over-cautious in their response to any injury? Even simpler, might he not actually be injured? As one MHR member stated (and this is a paraphrase) why risk him in a meaningless game?
Is it not possible (and I know those who dislike McDaniels will jump all over this one) that Coach McD is geninuinely concerned about Marshall and is trying to structure the pre-season to position Marshall to be physically fit, and mentally ready for the season opener in Cincinnati?
Marshall himself has stated that his unhappiness is not about money, he has stated that he has issues with the medical staff, he has stated that he's not up to speed on the playbook. Hmmmm . . . give him time to heal and learn the playbook, sounds like a way to begin rebuilding trust to me.