A number of the outdoor practice pitches for both the Broncos and their Super Bowl opponents the Seattle Seahawks are currently frozen due to a snowstorm in New Jersey last week.
"We'll look at the fields and test the fields, and we brought our grounds crew people," Fox told reporters.
"I understand the indoor facility is very much like ours, except their field house is completed, which is a big difference. So we may or may not go in there.
"I'd prefer grass. It saves our players' legs. But if need be, we'll go indoors or on their synthetic surface."
The freezing conditions are expected to last until Sunday's match, which is being forecast as the coldest Super Bowl in history.