The gold medallist was filming a cycling programme for the Discovery Channel in the U.S. last July (10) when he was knocked off his bike by a truck in Arizona.
He was treated for a fractured skull as well as bleeding and swelling on the brain, but made a good recovery.
Cracknell now suffers problems with concentration, memory and his temper, and reveals he has been advised not to be alone with his two young children, seven-year-old son Croyde and two-year-old daughter Kiki, in case he accidentally leaves them in harm's way.
He tells Britain's Radio Times, "I feel a bit useless. I can't help out."
Cracknell also admits his injuries have affected his relationship with his TV presenter wife Beverley Turner, who is currently pregnant with the couple's third child.
He adds, "I regret that the injury has had such an impact on everyone. Bev and I talk about nothing else, which takes the fun out of our relationship. It must be hard for her.
"I would say that if we didn't have kids we would have broken up. Aside from the fact that Bev is upset by the changes she sees in me, which I can't see in myself, my condition is constantly on our minds. You can never get away from it, and that's been really hard."