LEGO City: Undercover download requires an external Wii U hard drive
"An external hard drive is required to download this software," the game's official site cautions. "Visit support.nintendo.com for information about storage options."
As acknowledged on Nintendo's support page, the basic 8GB Wii U console has just 3GB of free space after installing the mandatory system software. Those who own the 32GB Deluxe Set have approximately 25GB of free space available, so while it is possible to squeeze the game onto it, you may have to clear some space if you have previously downloaded other software or apps.