The Jamaican is aiming to beat his 100m world record of 9.58 seconds, but Mills believes that the London event may not be the place for him to do it.
"I don't believe it's impossible, but he would have to have the right conditions," Mills told Sky Sports News. "I'm not sure if London is going to be kind. I am talking about the weather."
Bolt, who holds the current world records over 100m and 200m, previously said that he intends to become "a living legend" by securing victory at the Olympics.
The three-time Olympic gold medalist will compete in his first 100m of the season at the Jamaica International Invitational in Kingston a week on Saturday.