The Azzurri arrive in London with their stunning opening win over France now a distant memory following defeats in Scotland and at home to Wales.
By contrast England are gunning for a first Grand Slam in a decade with all talk of an RBS 6 Nations decider against Wales in Cardiff next weekend.
And while Brunel admits fatigue could have been a factor in Italy's lacklustre showing against Wales he knows a similar performance will be punished by England.
"We started well but have been disappointed in how the next two matches went," he said.
"Against Wales we didn't play at the intensity we should have. I don't know whether it was because of tiredness but the attitude wasn't what I expect.
"Sunday's match will be important in that respect. If we're not at their level physically we can expect a hard afternoon and a heavy defeat."