Mullens did not play during the Jaguars' 20-13 loss at Denver on Sunday and reverted back to Jacksonville's practice squad Monday, per the NFL's official transaction log.
The veteran signal-caller would have been the next man up after starter Trevor Lawrence with Quinn Evers inactive, but the Jaguars didn't have to call Mullens' number in Week 2. Jacksonville can elevate him once more this season before he'd need to be signed to their 53-man roster to be eligible to play.