Hammett has made a tentative start to life in charge at BT Sport Cardiff Arms Park, picking up seven points from their opening five GUINNESS PRO12 games.
The same cannot be said, however, for Sunday's hosts who sit just one point off the top of the table after five straight wins.
But the Blues head coach - a former All Blacks hooker - knows a victory over Steve Tandy's side could go a long way for both the club and the individuals who take to the field on the day.
"I am going into a wee bit of the unknown now in terms of how my players feel about playing the Ospreys," Hammett told Wales Online.
"One thing is for sure though. If you are an international or trying to claim a stake in that autumn Test series, these are the games you want to perform in. They are absolutely critical.
"We know that's how it will be. There are good line-ups right across the field.
"We are realistic. We are not quite where we need to be if you compare it to them. That's honest.
"We know how tough it will be, but we are preparing to win this game this weekend. We want to keep going up."
One of those individuals is veteran prop Adam Jones, who joined from Ospreys this summer, and Hammett admits the 33-year-old has impressed since moving to the Welsh capital.
"He's been superb in terms of his work-rate and what he's doing," he added.
"I'm not saying he's the finished product. But in terms of where he's got to, he's been fantastic.
"He's lost five or six kilos, he's in a place where he hasn't been since 2010 and from a scrummaging perspective he's our number one.
"He has been superb in that area and in terms of driving the game. He's been around a long time. I've been impressed in the early stages."
Follow us on Facebook, join the conversation on Twitter, sign up to our YouTube channel for extensive match highlights and sign up for our newsletter for regular updates on the GUINNESS PRO12
Guinness PRO12
Suite 208, Alexandra House,
The Sweepstakes
Ballsbridge, Dublin 4, Ireland