Gregan retired from international rugby following the World Cup and there is now a host of number nines queuing up to claim the pivot role in the national side.
Valentine is aware of the quality of opposition he faces but is adamant he can answer the Wallabies' call.
"He (Gregan) is obviously a legend of the game for who he is and what he's done but he's left now and there are openings for number nines around Australia," Valentine said.
"I will be putting my hand up and I'm sure the other guys will as well."
Valentine, who has won four Test caps, is ready to overcome the disappointment of missing out on World Cup selection.
"I had a bit of a taste last year and was a bit disappointed after not making it this year so it's made me work harder to push my claims again," Valentine said.
"You don't really have a say in it so you've just got to perform on the field and hope you're lucky enough to get picked."
In the meantime, Valentine faces a tough duel against Brett Sheehan and Luke Burgess to win the half-back job at the Waratahs during the Super 14 season.
"We've spoken about it and agreed there is no point getting angry with each other because it's only going to put us off our own game.
"We'll all be giving it everything but also working together.
"There is always competition any year you play - whether it be for Australia, club footy, Super 14.
"There are two others guys out to push their claims for a starting spot so it isn't going to be easy."