Lock (forearm) was listed as a limited participant on Monday's estimated practice report, John Boyle of the Seahawks' official site reports.
It's unclear when Lock picked up the injury, given that he did not play a single snap during Sunday's 32-29 loss to San Francisco. He's got two more chances to increase his practice participation, but if he cannot play against the Broncos on Thursday, then Jalen Milroe would serve as the Seahawks' backup quarterback behind Sam Darnold.