A day earlier, running back Darrell Henderson also was put on the reserve/COVID list.
The Rams (8-4) play the division-leading Arizona Cardinals at State Farm Stadium on Monday Night Football.
Coach Sean McVay has said this season that, to his knowledge, all players on the roster are vaccinated, with one exception, and that lone player who is unvaccinated has since gained antibodies.
Vaccinated players who test positive for COVID-19 must receive two negative tests in 24 hours to be eligible to return to action.
It's unclear who will start if Havenstein cannot play Monday, though tackle Joe Noteboom would seem a likely option given his experience in a backup role at left tackle.
Deayon, who was promoted earlier this season from the practice squad, has since been a key role player in the secondary. If he is unavailable against the Cardinals, depth could be a concern given rookie cornerback Robert Rochell was placed on injured reserve Saturday because of a chest injury.
Sony Michel is expected to start at running back given the unlikelihood that Henderson, who McVay said Saturday was showing signs of illness, clears COVID protocols in time for kickoff.