A 12” crossover was placed vertically on a Tubular rack on the HIAB truck. In order to protect the threads of the Crossover from getting damage during travelling, the Driver attempted to push the crossover into a horizontal position with his left foot while standing with his right foot on the lubricator and holding the side gate of the HIAB truck. During this attempt, his right foot slipped from the lubricator, causing him to fall and hit his left wrist on another lubricator resulted in a hairline fracture.