The Blues, ninth in the GUINNESS PRO12 table, take on the French outfit on Saturday knowing a point will be enough to make it through their Challenge Cup pool.
But Grenoble, already out of the running for qualification to the quarter-finals, ran London Irish incredibly close last weekend in a 43-41 defeat.
And Hammett wants his troops to be wary of complacency.
"I was surprised by Grenoble's performance," he told Wales Online. "It's a real wake-up call because French teams are usually stronger at home.
"We had to work hard to break them down in the first game in Cardiff so we're under no illusion that it will be a tough game out there.
"Each player needs to understand what we are trying to achieve and what they need to do for that to happen and then implement it.
"That's the same week-in, week-out. It's still all about standards and what we are trying to achieve. This game is as important as last week and the week before that.
"But we should be confident in our game. We want to qualify for the quarter-finals and get a home tie. The only way to do that is getting a good win and hope that a few other results go our way."
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