"To be honest, straight after the Derby I would have been happy for his season to be over," says the Canterbury trainer.
"It had already been a long season and it was an incredible Derby and he was tired.
"So I eased right up on him and while I have kept him fit and happy, I haven't asked him for much since."
That was in evidence when Sheriff raced below his best at Addington last start and maybe again when he was a solid but hardly sensational second at the Cambridge workouts last Saturday.
"I was initially disappointed but Todd Mitchell drove him and rang me straight away to say it was a good run and I trust his opinion.
"And he is a Bettor's Delight, we know they can be different horses on raceday.
"So I think he will improve and come out on Saturday and be the good horse he is. But whether that is good enough to win, we will find out."
While the front line for the mobile mile looks one of the fastest of the day, McGrath says he may add pull-down blinds to Sheriff's gear to get him keen enough to work to the lead and then give driver Blair Orange a turbo button to hit at the top of the straight.
But with Pat's Delight drawn to be close by and Sicario having thrilled his connections with his work this week, anything below the Derby-winning version of Sheriff is going to have a huge fight on his hooves.
McGrath actually takes one of the three previous Jewels winners racing to Saturday's meeting, with Dizzy Miss Lizzy brilliant at this meeting last season but missing in action since.
She has had nine starts since her Jewels stunner, all this season for a fresh up win and a second in the Sires' Stakes Final, the other seven being unplaced and largely disappointing performances.
"She has been terrible for much of the season," is McGrath's blunt assessment. "But she has had all sorts of problems. She has been in season a lot and I think she is over that and she has actually worked the best she has in a long time this week.
"I think she might be back to something like her best."
From barrier two in the three-year-old Diamond, Dizzy Miss Lizzy has the option to try and lead and could even hand up to hot favourite Shez All Rock, which would make her a value place hope.
