Denver has one of the best O-lines in the league. I truly think that if there was any more risk to Manning versus any other QB his age, he wouldn't attempt to play.
I'm a Bronco fan, so I'm a bit biased... Pairing Manning with a good receiving corps, a top notch running game, and an up and coming defense (Miller, Dumerville, Bailey, Ayers)... Denver will be a tough team this year. Looking at their schedule, they'll have to be.
EDIT: GO BRONCOS!!!!