Boycotting offseason practices is the tactic most utilized by franchise players seeking some semblance of leverage in long-term negotiations.
Thomas has decided that the risk of injury in May or June trumps the prospect of immediately adding millions to his bank account.
"I'm getting my body right, still working through a little soreness in my Achilles," Thomas added Monday, "but I could run routes."
Although plagued by foot issues throughout his career, Thomas hasn't missed a game since Manning joined the Broncos in 2012.
If the sides find common ground, Thomas should end collecting roughly $30 million in guarantees on a deal worth between $13 million and $15 million annually.