Crazy he can power his way through the injury on offense but somehow on defense it is really holding him back
It's a lot easier to play through a lower-body injury on offense than it is on defense. On offense you can pick your moves and you know what you're doing with your body, you do the exact things that won't aggravate the injury. On defense you have to react to what the other guy does and move spontaneously, and so you can't protect the injury in the same way.
That being said, Luka is CLEARLY not in good shape and CLEARLY is not a good defender, even before the injury. If he had worked himself into shape and improved his defensive instincts and effort beforehand, then he'd look a lot better now injury or no injury.