But Ashton concedes that there are half a dozen players at his disposal who could take on the crucial fly-half role. Danny Cipriani, Charlie Hodgson and Toby Flood are in England's RBS 6 Nations squad, while Ryan Lamb and Shane Geraghty are in the England Saxons squad.
"A few years ago there was Wilkinson, Hodgson and no-one else for fly-half, and now there are another four players who could step in and do a good job," Ashton told BBC Radio Five Live's Sportsweek programme.
Ashton denied that Wilkinson is the first player he puts down on the teamsheet when deciding on his XV.
"We talk about every position every time before a game and, from that point of view, he is no different to anyone else," he added.
"I'm quite excited by the squad of players we've got and, if I compare now to where I was ahead of my first game, my thoughts on who is going to play now are a lot clearer."