It's a one-week delay: The Wii U version had been scheduled to launch April 19, the same day as the Xbox 360 and PlayStation 3 versions of the game. A Warner Bros. spokesperson did not give a reason for the delay.
We've reached out to Warner Bros. to ask if the delay applies only to the U.K., or to all of Europe, which has the same release date of April 19. All three versions of Injustice: Gods Among Us are still scheduled to launch tomorrow, April 16, in North America. You can check out the game's launch trailer here.