The 19-year-old joined West Bromwich Albion on a season-long loan last week just a year after completing an £18m move to Stamford Bridge.
Lukaku's playing time was limited with the Blues and he has made his resentment public.
"I couldn't see myself staying at Chelsea," said Lukaku. "I sacrificed a year of my career with them and didn't want to put up with it anymore. I am relieved to have found a solution.
"On the first day of pre-season I told the manager I wanted to leave. I got sick of watching the others from the bench. I lost my hunger for the game over the past year and wasted my time.
"Last season I was in the reserves alongside a young lad who had barely turned 15 and I asked myself what I was doing there."
Lukaku has 14 caps for his country.