Doom has scrambled the neuro impules in the Hulk and Colossus's mind before, dropping them where they stood.
Colossus was in an old issue of the X-men where Doom was protecting Arcade and the X-men thought they where being sneaky and invaded Doom's castle. Colossus was all like RAWR! and Doom said "Doom do not engage in fisticuffs" and touched his head and dropped him. The Grey Hulk wouldn't listen to Doom so Doom did something similar and dropped the Grey Hulk. unless the Hulk has some sort of protection, he would drop just as easily.