The postponement is due to ongoing contract tracing within the Pistons, meaning that the team does not have the league-minimum eight available players for Monday's game.
According to ESPN's Adrian Wojnarowski, the Pistons were watching pre-game film and preparing for the game with the Nuggets when they learned of the postponement. The league has recently made the decision to park teams who end up in this situation over a single test.
The game against the Nuggets would have been the Pistons' second of a five-city Western Conference trip. The remainder includes contests against the Utah Jazz (Tuesday), the Phoenix Suns (Friday), and the Los Angeles Lakers (Saturday). It is unclear at the moment whether or not Detroit will be able to play later this week.
This is now the 23rd postponement of the season and the first in February after 21 such instances last month.