The Ninja Turtles were battling Krang when he transported them from their dimension to the world in which Injustice 2 takes place. In their Multiverse ending, the Turtles return to their world to face off against Krang, Shredder, and the Foot, having enhanced abilities from their time in the Injustice universe. Leonardo is seen attacking him with a taxi.
He is also mentioned in some of the Turtles' dialogue.